leetcode-go/easy/189.go

package main

func rotate1st(nums []int, k int) {
	n := len(nums)
	k %= n
	tmp := append(nums[n-k:], nums[:n-k]...)
	copy(nums, tmp)
}

func rotate2nd(nums []int, k int) {
	tmp := make([]int, len(nums))
	copy(tmp, nums)
	n := len(nums)
	for i, v := range tmp {
		idx := (i + k) % n
		nums[idx] = v
	}
}

func rotate3rd(nums []int, k int) {
	n := len(nums)
	k %= n
	// [1 2 3] -> [3 2 1]
	for i, j := 0, n-k-1; i < j; i, j = i+1, j-1 {
		nums[i], nums[j] = nums[j], nums[i]
	}
	// [4 5 6 7] -> [7 6 5 4]
	for i, j := n-k, n-1; i < j; i, j = i+1, j-1 {
		nums[i], nums[j] = nums[j], nums[i]
	}
	// [3 2 1 7 6 5 4] -> [4 5 6 7 1 2 3]
	for i, j := 0, n-1; i < j; i, j = i+1, j-1 {
		nums[i], nums[j] = nums[j], nums[i]
	}
}

// func main() {
// 	arr := []int{1, 2, 3, 4, 5, 6, 7}
// 	rotate1st(arr, 4)
// 	fmt.Println(arr)
// }