Merge pull request #5218 from Util/branch-for-challenge-138

Add Raku, Perl, and C solutions for #138 by Bruce Gray

6 files changed, 657 insertions, 0 deletions

diff --git a/challenge-138/bruce-gray/blog.txt b/challenge-138/bruce-gray/blog.txt
new file mode 100644
index 0000000000..57f75a1ee3
--- /dev/null
+++ b/challenge-138/bruce-gray/blog.txt
@@ -0,0 +1 @@
+http://blogs.perl.org/users/bruce_gray/2021/11/twc-138-partition-free-weekends.html
diff --git a/challenge-138/bruce-gray/c/ch-2.c b/challenge-138/bruce-gray/c/ch-2.c
new file mode 100644
index 0000000000..083807a365
--- /dev/null
+++ b/challenge-138/bruce-gray/c/ch-2.c
@@ -0,0 +1,474 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+/*
+gcc -Wall -O3 c/ch-2.c
+
+Running with numeric command-line params:
+./a.out 36 1028956744 1028956743 1028956745
+    36 : 1
+    1028956744 : 1
+    1028956743 : 0
+    1028956745 : 0
+
+Run with no parameters to auto-test (runs in < 1 second):
+./a.out
+    All 3200 tests (through 1028956744) of known-good numbers    returned True  as expected
+    All 6223 tests (through 1028956744) of known-good numbers ±1 returned False as expected
+
+Run with a dash parameters to generate the all perfect-square numbers that can_partition_to_square
+from 0 to 1 million, which is a perfect match for https://oeis.org/A104113/b104113.txt :
+./a.out -
+    1 0
+    2 1
+    3 81
+    ...
+    406 999982000081
+    407 999998000001
+    408 1000000000000
+
+Note that this program does not even try to embrace the "you give me a perfect square,
+and I will try to partition to its root" input that is specified in the Task.
+This is C! We are only here for performance!
+Instead, every number tested and printed (except via '-' above) will *be* the root,
+and we will use the digits of that root's square to sum back to the specified root.
+
+*/
+
+
+unsigned long powers_of_10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000, 10000000000, 100000000000, 1000000000000, 10000000000000, 100000000000000, 1000000000000000, 10000000000000000, 100000000000000000, 1000000000000000000 };
+
+int can_partition_to_target ( unsigned long n, unsigned long target ) {
+    if (n == target) return 1;
+    if (n <  target) return 0;
+
+    unsigned long right = 0;
+    unsigned long left  = n;
+    unsigned long digit;
+    for ( unsigned long *p = &powers_of_10[0] ; n >= *p ; ++p ) {
+        digit  = left % 10;
+        left  -= digit;
+        left  /= 10;
+        right += (digit * *p);
+
+        if (target < right) {
+            break; // guard against the unsigned subtraction below.
+        }
+
+        if (can_partition_to_target(left, target - right))
+            return 1;
+    }
+
+    return 0;
+}
+
+int can_partition_to_square ( unsigned int n ) {
+    unsigned long n2 = n;
+    n2 *= n2;
+    return can_partition_to_target(n2, n);
+}
+
+void print_all_that_can_partition ( ) {
+    const unsigned int limit = 1000000 + 1; // 1M = 5s O0, 0.8s O3
+    printf("Calculating for 0 .. %u\n", limit-1);
+    unsigned int count = 1;
+    for ( unsigned int i = 0 ; i < limit; i++ ) {
+        if ( can_partition_to_square(i) ) {
+            unsigned long square = i;
+            square *= square;
+            printf("%u %lu\n", count++, square);
+        }
+    }
+}
+
+void test_known_good_and_bad ( ) {
+    // From https://oeis.org/A038206/b038206.txt (the b-file for https://oeis.org/A038206/ )
+    // raku -e 'say .fmt("%8d,", "") for lines.map(*.words[1]).batch(10)' b038206.txt
+    const unsigned int b_data[] = { 
+               0,       1,       9,      10,      36,      45,      55,      82,      91,      99,
+             100,     235,     297,     369,     370,     379,     414,     657,     675,     703,
+             756,     792,     909,     918,     945,     964,     990,     991,     999,    1000,
+            1296,    1702,    1782,    2223,    2728,    3366,    3646,    3682,    4132,    4879,
+            4906,    4950,    5050,    5149,    5292,    6832,    7191,    7272,    7389,    7533,
+            7543,    7587,    7777,    7956,    8416,    8443,    8767,    8856,    8910,    8938,
+            9208,    9315,    9325,    9586,    9621,    9640,    9765,    9901,    9909,    9918,
+            9945,    9955,    9964,    9990,    9991,    9999,   10000,   10512,   12222,   12727,
+           17271,   17344,   22222,   22231,   25354,   27414,   33669,   34327,   35442,   36558,
+           36855,   38962,   39420,   41149,   41814,   42643,   45657,   46279,   48790,   48835,
+           49492,   49563,   49906,   50050,   51454,   52920,   52965,   53415,   57393,   57547,
+           59284,   62146,   64341,   65242,   67132,   68428,   69058,   69157,   69669,   72612,
+           74647,   75331,   76851,   77121,   77716,   77778,   77896,   79516,   81118,   82045,
+           82620,   82656,   85212,   85941,   87571,   88768,   88812,   88813,   89632,   90819,
+           91756,   93402,   93574,   94141,   94581,   95121,   97137,   99055,   99226,   99244,
+           99343,   99559,   99630,   99631,   99703,   99765,   99900,   99901,   99909,   99918,
+           99945,   99955,   99964,   99990,   99991,   99999,  100000,  104878,  105112,  105382,
+          117343,  122221,  130050,  131959,  140050,  142857,  143532,  148149,  163567,  167832,
+          172827,  181819,  187110,  203274,  208495,  215829,  249832,  275725,  283924,  304930,
+          310339,  316728,  318682,  319176,  320050,  329967,  333666,  336699,  336700,  336799,
+          338760,  339453,  344143,  349785,  351352,  352693,  354393,  356329,  356643,  357796,
+          364420,  364932,  369261,  369792,  370017,  370134,  370153,  383581,  389620,  389665,
+          390313,  410050,  417330,  417340,  419860,  428419,  434331,  440874,  441217,  452133,
+          452241,  461539,  463284,  466830,  471537,  473967,  474067,  482608,  490050,  499321,
+          499500,  499906,  500050,  500500,  501499,  512811,  514926,  524638,  529200,  529650,
+          532917,  533170,  534150,  536284,  538461,  549459,  551025,  552745,  561781,  571464,
+          584308,  584452,  596619,  600633,  609687,  627372,  627615,  639739,  642078,  643357,
+          643672,  647029,  648648,  649782,  656244,  668332,  670033,  670050,  673651,  675037,
+          681318,  684099,  689778,  695071,  697834,  713241,  719280,  736687,  739863,  751249,
+          754821,  758475,  758863,  760050,  770050,  780697,  784297,  789589,  790372,  791505,
+          791757,  792684,  795484,  798741,  804241,  805014,  810819,  811305,  812890,  818181,
+          825886,  826074,  831672,  831718,  834166,  836127,  836172,  847629,  849520,  850546,
+          851851,  852165,  852517,  853542,  853867,  857143,  857151,  860050,  865242,  872146,
+          877501,  880749,  887824,  888363,  889642,  890046,  906427,  906796,  907740,  908235,
+          910719,  919180,  920494,  921528,  921969,  929566,  935785,  940050,  945649,  945819,
+          948411,  949231,  951049,  951210,  952335,  955351,  961038,  961039,  968256,  968760,
+          969669,  977769,  987391,  989901,  990099,  991144,  991233,  991584,  992467,  992611,
+          993168,  994482,  994708,  994851,  994950,  996634,  998218,  998298,  998704,  999001,
+          999009,  999010,  999036,  999055,  999082,  999091,  999208,  999244,  999297,  999325,
+          999343,  999586,  999621,  999630,  999631,  999703,  999765,  999900,  999901,  999909,
+          999918,  999945,  999955,  999964,  999990,  999991,  999999, 1000000, 1005291, 1020304,
+         1038961, 1050957, 1051219, 1051246, 1074277, 1091197, 1100412, 1142856, 1148148, 1181818,
+         1187109, 1208494, 1226341, 1269918, 1300050, 1308385, 1318681, 1327150, 1329966, 1351351,
+         1356642, 1356966, 1390312, 1400050, 1461556, 1465093, 1635670, 1637694, 1643356, 1648647,
+         1670032, 1673820, 1681317, 1743966, 1782756, 1839601, 1865286, 1885869, 1907740, 1939572,
+         1952335, 2020446, 2026458, 2050624, 2078650, 2137338, 2307178, 2310894, 2371437, 2499832,
+         2579391, 2604583, 2671615, 2853469, 2866581, 3002454, 3022650, 3089872, 3100050, 3113829,
+         3161196, 3200050, 3212668, 3217347, 3245374, 3274641, 3336669, 3385530, 3441430, 3463786,
+         3469105, 3505617, 3558340, 3563335, 3582712, 3688597, 3696300, 3701197, 3701439, 3701493,
+         3701511, 3701529, 3701538, 3701556, 3704572, 3706354, 3718026, 3733273, 3848823, 3951549,
+         3980251, 3996541, 4042872, 4042945, 4100050, 4119966, 4126186, 4129218, 4158487, 4173408,
+         4187152, 4188303, 4221874, 4235842, 4238092, 4241512, 4292892, 4327867, 4395952, 4444444,
+         4454721, 4501611, 4522222, 4531275, 4647403, 4748131, 4776651, 4803624, 4811248, 4857786,
+         4894741, 4900050, 4927941, 4933045, 4983471, 4994298, 4999321, 4999906, 5000050, 5000500,
+         5002236, 5020921, 5050207, 5053222, 5072059, 5086756, 5088763, 5136570, 5160286, 5236911,
+         5246299, 5246388, 5253841, 5325228, 5364109, 5375736, 5401342, 5403277, 5413599, 5413644,
+         5467509, 5479453, 5527414, 5555556, 5642469, 5725882, 5881159, 5900050, 5913171, 5960503,
+         5973543, 6038983, 6045957, 6089778, 6104179, 6110766, 6188590, 6193701, 6209829, 6276150,
+         6276195, 6296382, 6308848, 6310809, 6313726, 6337458, 6364341, 6449409, 6472999, 6480945,
+         6530931, 6538644, 6557176, 6582241, 6595596, 6597019, 6607629, 6643242, 6651253, 6671332,
+         6682087, 6700050, 6721363, 6727312, 6728805, 6742954, 6780618, 6784767, 6790248, 6832513,
+         6844213, 6844221, 6844240, 6844285, 6848127, 6851323, 6905836, 6911361, 6938254, 6942744,
+         6946722, 6978376, 7006708, 7032546, 7050178, 7053868, 7080048, 7117381, 7198741, 7205950,
+         7223247, 7235830, 7333030, 7373593, 7395418, 7398639, 7412472, 7428151, 7449661, 7474941,
+         7505244, 7513156, 7533478, 7556041, 7558939, 7588017, 7588639, 7588675, 7588683, 7588720,
+         7600050, 7601985, 7657929, 7700050, 7757416, 7812540, 7834429, 7854165, 7869421, 7895935,
+         7915834, 7987374, 7987411, 7997292, 7997374, 8007372, 8040403, 8047666, 8049780, 8085843,
+         8092261, 8112412, 8161912, 8187265, 8199280, 8210592, 8235505, 8239077, 8263314, 8285985,
+         8286633, 8356771, 8365158, 8416269, 8416746, 8454852, 8492635, 8499294, 8514567, 8526069,
+         8537293, 8566129, 8600050, 8605143, 8647111, 8659207, 8709850, 8710398, 8757144, 8770797,
+         8773371, 8835490, 8878248, 8880309, 8881516, 8881524, 8903242, 8967736, 8971606, 8994411,
+         9050922, 9064486, 9078031, 9083169, 9122499, 9127863, 9142849, 9149464, 9186903, 9189181,
+         9360261, 9367155, 9372385, 9400050, 9417582, 9428554, 9432891, 9450541, 9453807, 9454869,
+         9455464, 9455581, 9457704, 9457974, 9458227, 9458235, 9472536, 9495828, 9565336, 9610380,
+         9625537, 9634843, 9639450, 9666999, 9674541, 9677808, 9685485, 9685540, 9688618, 9693766,
+         9726112, 9745488, 9785781, 9835263, 9869077, 9873955, 9878679, 9879210, 9898956, 9898983,
+         9898984, 9912429, 9922879, 9923149, 9942453, 9944820, 9947080, 9949617, 9951165, 9969669,
+         9990360, 9990685, 9991062, 9991090, 9991557, 9992044, 9992413, 9992457, 9992611, 9992809,
+         9995094, 9995868, 9996318, 9996354, 9997272, 9997777, 9998218, 9998298, 9998704, 9999000,
+         9999001, 9999009, 9999010, 9999036, 9999055, 9999082, 9999091, 9999208, 9999244, 9999297,
+         9999325, 9999343, 9999586, 9999621, 9999630, 9999631, 9999703, 9999765, 9999900, 9999901,
+         9999909, 9999918, 9999945, 9999955, 9999964, 9999990, 9999991, 9999999,10000000,10122634,
+        10273807,10300050,10379196,10400050,10512487,10627614,10656712,11004535,11111112,11200050,
+        11300050,11336284,11451861,11786094,11881909,12100050,12200050,12966481,13000050,13100050,
+        13165273,13165794,13641364,13798963,13809060,13809105,13900050,14000050,14649417,14650677,
+        14650966,14776651,14800050,14882481,14900050,15700050,15800050,15940143,16486858,16590564,
+        16600050,16678332,17600050,17645401,17645446,17793918,17827722,17938611,18181909,18400050,
+        18453142,19273023,19300050,19400050,19440729,19773073,20300050,20644767,20658195,21091591,
+        21200050,22056795,22100050,22385763,22633227,22692780,22866256,23102074,23358582,23493052,
+        23502132,23714370,23800050,23900050,24459039,24700050,24752475,24800050,24944437,24999832,
+        25027435,25252525,25389235,25545132,25600050,25700050,25947244,26126856,26436672,26600050,
+        26670888,26695872,27099685,27342910,27400050,27500050,27684423,27798912,27843822,28137870,
+        28141398,28300050,28400050,28487160,28788688,28970497,29200050,29330757,29375794,30200050,
+        30600775,30884184,31000050,31033891,31100050,31591638,31603032,31900050,31958091,32000050,
+        32000500,32126724,32126725,32192442,32461758,32800050,32900050,33216444,33336666,33366699,
+        33366700,33524587,33602365,33605595,33650208,33664473,33700050,33800050,33813910,34192972,
+        34600050,34700050,34910290,35144227,35144613,35144622,35144623,35500050,35546508,35600050,
+        35602578,35851897,35941833,36175969,36212733,36240849,36271765,36363636,36400050,36487873,
+        36496351,36500050,36792379,36942346,36943426,37015344,37015497,37015507,37015534,37015551,
+        37015588,37015605,37015606,37206577,37300050,37466470,37605060,37630963,37651212,37918674,
+        37919908,38097144,38178298,38200050,38267586,38440180,38883889,39100050,39142549,39200050,
+        39451735,39527146,39565081,39802510,39825604,40057966,40100050,40140784,40229371,40427766,
+        40458258,40503123,40503124,40546944,40900050,40913937,41000050,41159628,41186799,41228317,
+        41608764,41734081,41800050,41884534,41900050,42229090,42476436,42584338,42616774,42700050,
+        42783499,42800050,42894478,43033887,43046487,43064406,43091712,43365232,43497451,43600050,
+        43795621,43855894,43923007,44091856,44345512,44363341,44365158,44434710,44500050,44525548,
+        44659440,44685064,44859943,44871426,45027217,45224146,45224154,45268822,45400050,45403237,
+        45436267,45501039,45512037,45534897,45559791,45776170,46179405,46300050,46400050,46886859,
+        47200050,47300050,47406816,47406817,47428623,47494576,47514915,47943649,48100050,48419874,
+        48435058,48461166,48502422,48516508,48949453,49000050,49000500,49100050,49106935,49315159,
+        49995000,49999321,49999906,50000050,50000500,50005000,50014999,50502483,50537169,50589036,
+        50672124,50728222,50729868,50765491,50787433,50800050,50900050,50955382,51120946,51333525,
+        51456177,51492646,51800050,52131772,52299423,52315822,52463925,52463926,52824204,53252280,
+        53500050,53863462,54500050,54794530,54794575,54870346,54922159,55012041,55274022,55274185,
+        55300050,55314523,55400050,55474452,55499059,55636659,56076525,56200050,56478870,56502550,
+        57200050,57321306,57347542,57347587,57424509,57511521,57669462,57754459,57768138,57789081,
+        57860676,58100050,58236894,58569229,58811490,58811661,58811662,58900050,59000050,59066866,
+        59334588,59509377,59715756,59775913,59800050,59889366,59900050,59973543,59977809,60421735,
+        60469866,60548275,60632632,60885352,60913854,61116111,61758936,61785324,61884262,62017713,
+        62146161,62165341,62174124,62326746,62388477,62500050,62526996,62584632,62606917,62647128,
+        62838568,62850321,62951967,62951977,63013699,63099865,63184932,63305505,63400050,63411642,
+        63554319,63636364,64284246,64300050,64354249,64400050,64934532,64968273,65088469,65200050,
+        65300050,65522566,65606140,65816911,66062592,66076291,66100050,66200050,66224727,66307338,
+        66683332,67000050,67309489,67568283,67639401,67690972,67900050,68000500,68195908,68325130,
+        68422834,68427631,68427676,68442211,68442588,68442768,68442814,68442858,68442867,68442876,
+        68442885,68460543,68707944,68800050,68900050,69042771,69058368,69058369,69115816,69200632,
+        69399226,69431220,69589647,69783832,69800050,69903720,70192728,70207389,70224121,70275214,
+        70406254,70501717,70578991,70653384,71025120,71157934,71408521,71408943,71500050,71534224,
+        71600050,72230347,72400050,72448839,72500050,72697780,72900316,72902188,72973828,73052929,
+        73084635,73194517,73258471,73670661,73692603,73875223,73889172,74002527,74060271,74200050,
+        74261313,74300050,74747475,75012499,75200050,75247525,75297762,75517399,75655954,75695158,
+        75725343,75748582,75868291,75870334,75887164,75887190,75887208,75887227,75919851,76000050,
+        76050954,76072834,76094064,76100050,76168810,76294152,76550779,76900050,77000050,77014107,
+        77098077,77151285,77607846,77800050,77813748,77900050,77961277,78092892,78126768,78340716,
+        78541695,78604047,78800050,78941610,79226209,79241625,79600050,79611264,79652035,79700050,
+        79719039,79785837,80137882,80226927,80500050,80501562,80546310,80548462,80628877,80692507,
+        80726977,80854776,80888059,80982028,80987536,81004122,81015067,81354664,81413397,81500050,
+        81528003,81530569,81570924,81619120,81619165,81872695,82110159,82207755,82269234,82512127,
+        82620307,82620864,82620865,82875132,82993122,83200050,83287206,83341666,83409436,83417760,
+        83476629,83567683,83665791,83773017,84100050,84167496,84229317,84367314,84766059,84894516,
+        84916719,85045329,85127464,85196943,85223350,85338667,85354281,85431511,85617459,85661290,
+        85694554,85797639,85807098,85824289,85898718,85918257,85925449,85941495,86000050,86332455,
+        86358636,86501871,86763285,86800050,86900050,86977351,87072337,87103935,87369831,87452127,
+        87457104,87657724,87685623,87738121,87757551,87785767,87914044,88047666,88251067,88418430,
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+        985385907,986371120,986907735,986980177,987246648,988204069,989898471,990037368,990208054,990504172,
+        990527464,990554923,990556696,990632845,992002708,992675521,992794050,992944081,993723805,994083588,
+        995000050,995873814,996182695,996242752,996886171,998134714,998256034,998498116,998513730,998538444,
+        998773659,999000999,999031501,999038961,999149454,999165834,999173926,999195759,999204516,999210411,
+        999280720,999286759,999310222,999331668,999352971,999357922,999372628,999428536,999498501,999499500,
+        999580140,999635068,999666334,999716076,999724275,999784171,999827173,999832168,999856468,999859950,
+        999869950,999900774,999902863,999905419,999905859,999906598,999909181,999911187,999911188,999911232,
+        999914059,999914788,999917380,999917955,999922104,999922284,999924669,999925353,999930843,999930942,
+        999931572,999932868,999937854,999940716,999942607,999950094,999950437,999957357,999958186,999960580,
+        999963145,999963442,999964396,999965673,999966331,999972586,999974646,999977769,999977778,999982656,
+        999982729,999987273,999987778,999989488,999990000,999990001,999990009,999990010,999990036,999990045,
+        999990055,999990082,999990091,999990099,999990235,999990360,999990379,999990414,999990675,999990685,
+        999990792,999991062,999991090,999991144,999991233,999991557,999991584,999992044,999992223,999992413,
+        999992457,999992467,999992611,999992728,999992809,999993168,999994708,999994851,999994950,999995050,
+        999995094,999995121,999995868,999996318,999996354,999996634,999997272,999997777,999998218,999998298,
+        999998704,999999000,999999001,999999009,999999010,999999036,999999055,999999082,999999091,999999208,
+        999999244,999999297,999999325,999999343,999999586,999999621,999999630,999999631,999999703,999999765,
+        999999900,999999901,999999909,999999918,999999945,999999955,999999964,999999990,999999991,999999999,
+        1000000000,1003000050,1004000050,1005012487,1012000050,1013000050,1020658195,1021000050,1022000050,1028956744,
+    };
+    const unsigned int b_data_last_index = sizeof(b_data) / sizeof(unsigned int) - 1;
+    const unsigned int last_number = b_data[b_data_last_index];
+
+    // Check every b038206 number to make sure it can partition.
+    int all_good_tests_OK = 1;
+    for ( const unsigned int *b = &b_data[0] ; b <= &b_data[b_data_last_index] ; ++b ) {
+        unsigned int known_good = *b;
+        if (can_partition_to_square(known_good) != 1) {
+            printf("Bad known_good: %d\n", known_good);
+            all_good_tests_OK = 0;
+        }
+    }
+    if (all_good_tests_OK) {
+        printf("All %d tests (through %u) of known-good numbers    returned True  as expected\n",
+            b_data_last_index+1, last_number);
+    }
+
+    // Check a number on either side of every b038206 number (except when that neighbor is also in b038206) to make sure it cannot partition.
+    int all_bad_tests_OK = 1;
+    int bad_test_count = 0;
+    for ( const unsigned int *b = &b_data[1] ; b < &b_data[b_data_last_index] ; ++b ) {
+        unsigned int this = *b;
+        unsigned int last = *(b-1);
+        unsigned int next = *(b+1);
+        unsigned int this_minus_one = this - 1;
+        unsigned int this_plus_one  = this + 1;
+        
+        if ( this_minus_one != last ) {
+            bad_test_count++;
+            if ( can_partition_to_square(this_minus_one) != 0) {
+                printf("Good known_bad: %d\n", this_minus_one);
+                all_bad_tests_OK = 0;
+            }
+        }
+        if (this_plus_one != next) {
+            bad_test_count++;
+            if ( can_partition_to_square(this_plus_one) != 0) {
+                printf("Good known_bad: %d\n", this_plus_one);
+                all_bad_tests_OK = 0;
+            }
+        }
+    }
+    if (all_bad_tests_OK) {
+        printf("All %d tests (through %u) of known-good numbers ±1 returned False as expected\n",
+            bad_test_count, last_number);
+    }
+
+}
+
+int main ( int argc, char *argv[] ) {
+    unsigned int arg_count = argc - 1;
+
+    if (arg_count == 0) {
+        test_known_good_and_bad();
+    }
+    else if (arg_count == 1 && argv[1][0] == '-') {
+        print_all_that_can_partition();
+    }
+    else {
+        for ( int arg_n = 1 ; arg_n < argc ; ++arg_n ) {
+            unsigned int arg = atol(argv[arg_n]);
+            printf("%d : %d\n", arg, can_partition_to_square(arg));
+        }
+    }
+    return 0;
+}
diff --git a/challenge-138/bruce-gray/perl/ch-1.pl b/challenge-138/bruce-gray/perl/ch-1.pl
new file mode 100644
index 0000000000..8a40cfb3f7
--- /dev/null
+++ b/challenge-138/bruce-gray/perl/ch-1.pl
@@ -0,0 +1,32 @@
+use Modern::Perl;
+use 5.026;
+use experimental qw<signatures>;
+use DateTime;
+
+sub is_working_day ($date) {
+    my $day = $date->day_of_week;
+    return !($day == 6 or $day == 7);
+}
+sub working_days_in_year ($year) {
+    my $d = DateTime->new(year => $year);
+
+    my $working_days_count = 0;
+    for (1 .. $d->year_length) {
+        $working_days_count++ if is_working_day($d);
+        $d->add(days => 1);
+    }
+    return $working_days_count;
+}
+
+use Test::More;
+my @tests = (
+    [ 2021, 261 ],
+    [ 2020, 262 ],
+);
+plan tests => 0+@tests;
+
+for (@tests) {
+    my ($input_year, $expected) = @{$_};
+    is working_days_in_year($input_year),   $expected,
+      "working_days_in_year($input_year) == $expected";
+}
diff --git a/challenge-138/bruce-gray/perl/ch-2.pl b/challenge-138/bruce-gray/perl/ch-2.pl
new file mode 100644
index 0000000000..ff16eb3237
--- /dev/null
+++ b/challenge-138/bruce-gray/perl/ch-2.pl
@@ -0,0 +1,78 @@
+use strict;
+use warnings;
+use 5.026;
+
+use experimental qw<signatures>;
+use ntheory      qw<forcomp>;
+use List::Util   qw<sum>;
+use Test::More;
+
+use Memoize;
+memoize('templates_for_size');
+
+#   templates_for_size(3) returns ['a1 a1 a1',   'a1 a2',   'a2 a1',   'a3']
+sub templates_for_size ( $size ) {
+    my @r;
+
+    forcomp { push @r, join ' ', map "a$_", @_ } $size;
+
+    return \@r;
+}
+
+#   partition_sums(789) returns (24, 96, 87, 789) because '7'+'8'+'9'=24, '7'+'89'=96, '78'+'9'=87, and '789'=789
+sub partition_sums ( $n ) {
+    my $unpack_templates_aref = templates_for_size(length $n);
+
+    return map { sum unpack $_, $n } @{$unpack_templates_aref};
+}
+
+sub can_partition_to_sqrt ( $n ) {
+    my $r = int sqrt $n;
+    die "$n is not a perfect square" if $r ** 2 != $n;
+
+    return 0 + !! grep { $_ == $r } partition_sums($n);
+}
+
+
+my @tests = (
+    # From examples in task description:
+    [    81, 1 ],
+    [  9801, 1 ],
+    [    36, 0 ],
+
+    # Regression tests
+    [     72 ** 2, 0 ],
+
+    [     36 ** 2, 1 ], # 36² == 1296,  1+29+6 == 36. Finds single-sided insufficient algorithms.
+    [ 165607 ** 2, 0 ],
+
+    # From the far edge of https://oeis.org/A038206/b038206.txt :
+    [ 1028956743 ** 2, 0 ],
+    [ 1028956744 ** 2, 1 ],
+    [ 1028956745 ** 2, 0 ],
+
+);
+
+
+use constant USE_LONG_TESTS => 1;
+plan tests => @tests + (USE_LONG_TESTS ? 2 : 0);
+
+for (@tests) {
+    my ( $input, $expected ) = @{$_};
+    is can_partition_to_sqrt($input),   $expected,
+      "can_partition_to_sqrt($input) == $expected";
+}
+
+if (USE_LONG_TESTS) {
+    # The squares for which can-partition-to-sqrt returns True are an OEIS sequence.
+    # The square-roots of those squares are also an OEIS sequence.
+    # Test all the elements given on the OEIS web pages. (49 elements, and 35 elements).
+    use constant