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E

tags: Array, Rotation

#### Rotate array in place

- rotate all

- rotate 2 sides: < k or >=

#### Rotate by buffer the k array

```

/*

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?

*/

/*

1. rotate all

1. rotate 2 sides: < k or >= k

*/

class Solution {

public void rotate(int[] nums, int k) {

int n = nums.length;

k = k % n;

if (k == 0) return;

// rotate all

rotateByRange(nums, 0, n - 1);

// rotate side

rotateByRange(nums, 0, k - 1);

rotateByRange(nums, k, n - 1);

}

private void rotateByRange(int[] nums, int x, int y) {

while (x >= 0 && x < y) {

int temp = nums[x];

nums[x] = nums[y];

nums[y] = temp;

x++;

y--;

}

}

}

```