Merge pull request #4992 from ealvar3z/branch-for-challenge-132

go solutions with wiki & abigail's blog post

3 files changed, 137 insertions, 0 deletions

diff --git a/challenge-132/ealvar3z/README.md b/challenge-132/ealvar3z/README.md
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+++ b/challenge-132/ealvar3z/README.md
@@ -0,0 +1 @@
+Solutions by ealvar3z
diff --git a/challenge-132/ealvar3z/go/ch-1.go b/challenge-132/ealvar3z/go/ch-1.go
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index 0000000000..5d7f04fc3d
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+++ b/challenge-132/ealvar3z/go/ch-1.go
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+package main
+
+//  functions come from [wiki](https://en.wikipedia.org/wiki/Julian_day#Julian_day_number_calculation)
+//  translated from [abigail's Perl blog post](https://abigail.github.io/HTML/Perl-Weekly-Challenge/week-132-1.html)
+
+import (
+	"fmt"
+	"log"
+)
+
+// Gregorian to Julian calendar converter
+func g2j(Y, M, D int64) int64 {
+	return ((1461*(Y+4800+(M-14)/12))/4 +
+		(367*(M-2-12*((M-14)/12)))/12 -
+		(3*((Y+4900+(M-14)/12)/100))/4 + D - 32075)
+}
+
+// Julian to Gregorian calendar converter
+func j2g(jd int64) []int64 {
+	e := 4*(jd+1401+(((4*jd+274277)/146097)*3)/4-38) + 3
+	D := ((5*((e%1461)/4)+2)%153)/5 + 1
+	M := (((5*((e%1461)/4)+2)/153 + 2) % 12) + 1
+	Y := (e / 1461) - 4716 + (12+2-M)/12
+	return []int64{Y, M, D}
+}
+
+var today = []uint{2021, 9, 22} // using this date for testing
+
+func main() {
+	//read in the input date
+	var Y, M, D int64
+	fmt.Println("input yr, mon, and date on each line") // Question to the user
+	if _, err := fmt.Scan(&Y, &M, &D); err != nil {
+		log.Println(err)
+	}
+
+	today_y := int64(today[0])
+	today_m := int64(today[1])
+	today_d := int64(today[2])
+
+	julian_2day := g2j(today_y, today_m, today_d)
+	julian_then := g2j(Y, M, D)
+	then := j2g(2*julian_then - julian_2day)
+	now := j2g(2*julian_2day - julian_then)
+	fmt.Printf("%04d/%02d/%02d => %04d/%02d/%02d\n", then[0], then[1], then[2], now[0], now[1], now[2])
+}
diff --git a/challenge-132/ealvar3z/go/ch-2.go b/challenge-132/ealvar3z/go/ch-2.go
new file mode 100644
index 0000000000..b0b1f6f5fb
--- /dev/null
+++ b/challenge-132/ealvar3z/go/ch-2.go
@@ -0,0 +1,90 @@
+package main
+
+/*
+Write a script to implement Hash Join algorithm as suggested by wikipedia.
+
+The "hash join" algorithm consists of two steps:
+
+1. Hash phase:
+ 1.1 - Create a multimap from one of the two tables, mapping from each join column value to all the rows that contain it. The multimap must support hash-based lookup which scales better than a simple linear s earch, because that's the whole point of this algorithm. Ideally we should create the multimap for the  smaller table, thus minimizing its creation time and memory size.
+
+2. Join phase:
+ 2.1 - Scan the other table, and find matching rows by looking in the multimap created before.
+
+Test Case
+
+Input:
+
+    @player_ages = (
+        [20, "Alex"  ],
+        [28, "Joe"   ],
+        [38, "Mike"  ],
+        [18, "Alex"  ],
+        [25, "David" ],
+        [18, "Simon" ],
+    );
+
+    @player_names = (
+        ["Alex", "Stewart"],
+        ["Joe",  "Root"   ],
+        ["Mike", "Gatting"],
+        ["Joe",  "Blog"   ],
+        ["Alex", "Jones"  ],
+        ["Simon","Duane"  ],
+    );
+
+Output:
+
+    Based on index = 1 of @players_age and index = 0 of @players_name.
+
+    20, "Alex",  "Stewart"
+    20, "Alex",  "Jones"
+    18, "Alex",  "Stewart"
+    18, "Alex",  "Jones"
+    28, "Joe",   "Root"
+    28, "Joe",   "Blog"
+    38, "Mike",  "Gatting"
+    18, "Simon", "Duane"
+
+*/
+
+import "fmt"
+
+func main() {
+	playerAges := []struct {
+		value int
+		key   string
+	}{
+		{20, "Alex"},
+		{28, "Joe"},
+		{38, "Mike"},
+		{18, "Alex"},
+		{25, "David"},
+		{18, "Simon"},
+	}
+
+	playerNames := []struct {
+		key   string
+		value string
+	}{
+		{"Alex", "Stewart"},
+		{"Joe", "Root"},
+		{"Mike", "Gatting"},
+		{"Joe", "Blog"},
+		{"Alex", "Jones"},
+		{"Simon", "Duane"},
+	}
+
+	// build the hash phase
+	h := map[string][]int{}
+	for n, a := range playerAges {
+		h[a.key] = append(h[a.key], n)
+	}
+
+	// join phase
+	for _, i := range playerNames {
+		for _, j := range h[i.key] {
+			fmt.Println("Based on index = 1 of", playerAges[j], "and index = 0 of", i.value)
+		}
+	}
+}