Data commit

Task/Permutations/Go/permutations-1.go

@@ -0,0 +1,52 @@
+package main
+
+import "fmt"
+
+func main() {
+    demoPerm(3)
+}
+
+func demoPerm(n int) {
+    // create a set to permute.  for demo, use the integers 1..n.
+    s := make([]int, n)
+    for i := range s {
+        s[i] = i + 1
+    }
+    // permute them, calling a function for each permutation.
+    // for demo, function just prints the permutation.
+    permute(s, func(p []int) { fmt.Println(p) })
+}
+
+// permute function.  takes a set to permute and a function
+// to call for each generated permutation.
+func permute(s []int, emit func([]int)) {
+    if len(s) == 0 {
+        emit(s)
+        return
+    }
+    // Steinhaus, implemented with a recursive closure.
+    // arg is number of positions left to permute.
+    // pass in len(s) to start generation.
+    // on each call, weave element at pp through the elements 0..np-2,
+    // then restore array to the way it was.
+    var rc func(int)
+    rc = func(np int) {
+        if np == 1 {
+            emit(s)
+            return
+        }
+        np1 := np - 1
+        pp := len(s) - np1
+        // weave
+        rc(np1)
+        for i := pp; i > 0; i-- {
+            s[i], s[i-1] = s[i-1], s[i]
+            rc(np1)
+        }
+        // restore
+        w := s[0]
+        copy(s, s[1:pp+1])
+        s[pp] = w
+    }
+    rc(len(s))
+}

Task/Permutations/Go/permutations-2.go

@@ -0,0 +1,29 @@
+package main
+
+import "fmt"
+
+func main() {
+        var a = []int{1, 2, 3}
+        fmt.Println(a)
+        var n = len(a) - 1
+        var i, j int
+        for c := 1; c < 6; c++ { // 3! = 6:
+                i = n - 1
+                j = n
+                for a[i] > a[i+1] {
+                        i--
+                }
+                for a[j] < a[i] {
+                        j--
+                }
+                a[i], a[j] = a[j], a[i]
+                j = n
+                i += 1
+                for i < j {
+                        a[i], a[j] = a[j], a[i]
+                        i++
+                        j--
+                }
+                fmt.Println(a)
+        }
+}