Next Permutation.go

import (
	"strings"
	"strconv"
)

func nextPermutation(nums []int)  {
	var startPoint = -1
	var endPoint = -1

	// find start point
	lenOfNums := len(nums)
	for idx := lenOfNums - 2; idx >= 0; idx-- {
		if nums[idx] < nums[idx + 1] {
			startPoint = idx
			break
		}
	}

	if -1 != startPoint {
		// find end point
		for idx := startPoint + 1; idx < lenOfNums; idx++ {
			if nums[startPoint] < nums[idx] && (-1 == endPoint || nums[idx] <= nums[endPoint]) {
				endPoint = idx
			}
		}

		// swap
		nums[startPoint], nums[endPoint] = nums[endPoint], nums[startPoint]
	}

	// reverse post part of array
	halfOfNumOfReverse := (lenOfNums - startPoint - 1) / 2
	for idx := 1; idx <= halfOfNumOfReverse; idx++ {
		oneIdx := startPoint + idx
		anotherIdx := lenOfNums - idx
		nums[oneIdx], nums[anotherIdx] = nums[anotherIdx], nums[oneIdx]
	}

	// print results
	var outputs []string
	for _, i := range nums {
		outputs = append(outputs, strconv.Itoa(i))
	}

	println(strings.Join(outputs, " "))
}