189. Rotate Array

Description

Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: [1,2,3,4,5,6,7] and k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]
Example 2:

Input: [-1,-100,3,99] and k = 2
Output: [3,99,-1,-100]
Explanation:
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]
Note:

Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.
Could you do it in-place with O(1) extra space?

Answer

package main

import "fmt"

func rotate(nums []int, k int) {
    k = k % len(nums)
    reverse(nums, 0, len(nums))
    reverse(nums, 0, k)
    reverse(nums, k, len(nums))

}

func reverse(nums []int, start, end int) {
    for start < end {
        nums[start], nums[end-1] = nums[end-1], nums[start]
        start++
        end--
    }
}

func main() {
    a := []int{-1, 2, 3}
    rotate(a, 4)
    fmt.Println(a)
}