Find Kth Permutation

Author: gokivego

MathAndStats/FindKthPermutation.go

@@ -0,0 +1,53 @@
+/*
+Find the Kth Permutation of a given number
+*/
+
+package main
+
+import ("fmt")
+
+func Factorial(n int) int {
+ var FactorialArray = []int{1,1}
+ if n == 0 || n == 1 {return 1}
+ for i:=2;i<n+1;i++ {
+ FactorialArray = append(FactorialArray,i*FactorialArray[i-1])
+ }
+ return FactorialArray[n]
+}
+
+func Remove(array []int,index int) []int {
+ if index >= len(array) {
+ return array
+ } else {
+ return append(array[:index],array[index+1:]...)
+ }
+}
+
+func FindKthPermutation(num []int,k int,) *[]int {
+ var KthPermutation []int
+ t := len(num)
+ num1 := num
+ if k > Factorial(len(num)) {
+ KthPermutation = append(KthPermutation,-1)
+ return &KthPermutation
+ }
+ for i:=0;i<len(num);i++ {
+ blockSize := Factorial(t-1)
+ selected := (k-1)/blockSize
+ //fmt.Println(num1)
+ //fmt.Println(selected)
+ KthPermutation = append(KthPermutation,num1[selected])
+ num1 = Remove(num1,selected) // The array is shrinking with every iteration
+ k = k -selected*blockSize
+ t--
+ }
+ return &KthPermutation
+}
+
+
+func main() {
+ array := []int{1,2,3,4}
+ KthPermutationPtr := FindKthPermutation(array,8)
+ fmt.Println(*KthPermutationPtr)
+}
+