Add Forth solution to challenge 102

2 files changed, 94 insertions, 0 deletions

diff --git a/challenge-102/paulo-custodio/forth/ch-1.fs b/challenge-102/paulo-custodio/forth/ch-1.fs
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+#! /usr/bin/env gforth
+
+\ Challenge 102
+\
+\ TASK #1 › Rare Numbers
+\ Submitted by: Mohammad S Anwar
+\
+\ You are given a positive integer $N.
+\
+\ Write a script to generate all Rare numbers of size $N if exists. Please
+\ checkout the page for more information about it.
+\ Examples
+\
+\ (a) 2 digits: 65
+\ (b) 6 digits: 621770
+\ (c) 9 digits: 281089082
+
+\ 1234 -> 4321
+: invert_number     { n -- }
+    0 { n1 }
+    BEGIN n 0<> WHILE
+        n1 10 *  n 10 MOD  +  TO n1
+        n 10 /  TO n
+    REPEAT
+    n1 ;
+
+\ check if number is perfect square
+: is_perfect_square ( n -- f )
+    S>F FSQRT
+    FDUP FLOOR F= IF TRUE ELSE FALSE THEN ;
+
+\ compute 10^n
+: 10pow     ( n -- 10^n )
+    1 SWAP
+    0 ?DO
+        10 *
+    LOOP ;
+
+: .rare { n -- }
+    n 10pow  n 1- 10pow DO
+        I I invert_number       { r r1 }
+        r r1 + is_perfect_square IF
+            r r1 >= IF
+                r r1 - is_perfect_square IF
+                    r . CR
+        THEN THEN THEN
+    LOOP ;
+
+NEXT-ARG S>NUMBER? 0= THROW DROP
+.rare
+BYE
diff --git a/challenge-102/paulo-custodio/forth/ch-2.fs b/challenge-102/paulo-custodio/forth/ch-2.fs
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+#! /usr/bin/env gforth
+
+\ Challenge 102
+\
+\ TASK #2 › Hash-counting String
+\ Submitted by: Stuart Little
+\
+\ You are given a positive integer $N.
+\
+\ Write a script to produce Hash-counting string of that length.
+\
+\ The definition of a hash-counting string is as follows:
+\ - the string consists only of digits 0-9 and hashes, ‘#’
+\ - there are no two consecutive hashes: ‘##’ does not appear in your string
+\ - the last character is a hash
+\ - the number immediately preceding each hash (if it exists) is the position
+\ of that hash in the string, with the position being counted up from 1
+\
+\ It can be shown that for every positive integer N there is exactly one such
+\ length-N string.
+\ Examples:
+\
+\ (a) "#" is the counting string of length 1
+\ (b) "2#" is the counting string of length 2
+\ (c) "#3#" is the string of length 3
+\ (d) "#3#5#7#10#" is the string of length 10
+\ (e) "2#4#6#8#11#14#" is the string of length 14
+
+\ hash-counting - use <# #> buffer to build string
+: .hash_counting     { i -- }
+    0. <#
+    BEGIN i 0> WHILE
+        i { pos }
+        '#' HOLD        i 1- TO i
+        BEGIN i 0> pos 0<> AND WHILE
+            2DROP pos 0 #     i 1- TO i
+            OVER TO pos
+        REPEAT
+    REPEAT
+    #> TYPE ;
+
+NEXT-ARG S>NUMBER? 0= THROW DROP
+.hash_counting CR BYE