updated util packages

algos/permutations.go

@@ -0,0 +1,34 @@
+package algos
+
+// MakePermutations will make all permutations of the numbers input
+// returns a pointer to avoid copying a large number of permutations
+func MakePermutations(numbers []int) *[][]int {
+	result := make([][]int, 0)
+
+	swapRecurseBacktrack(numbers, 0, &result)
+
+	return &result
+}
+
+// helper function to generate permutations
+func swapRecurseBacktrack(numbers []int, startIndex int, results *[][]int) {
+	if startIndex == len(numbers) {
+		// make a copy of the perm
+		perm := make([]int, len(numbers))
+		copy(perm, numbers)
+
+		// assign the value at the pointer results to the appended slice (dereferenced) results w/ perm
+		*results = append(*results, perm)
+	}
+
+	for i := startIndex; i < len(numbers); i++ {
+		// swap numbers
+		numbers[startIndex], numbers[i] = numbers[i], numbers[startIndex]
+
+		// recurse with startIndex incremented
+		swapRecurseBacktrack(numbers, startIndex+1, results)
+
+		// backtrack
+		numbers[startIndex], numbers[i] = numbers[i], numbers[startIndex]
+	}
+}