189. Rotate Array

,

Math

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
class Solution {
    public void rotate(int[] nums, int k) {
        k %= nums.length;

        if (k == 0) {
            return;
        }

        for (int i = 0; i < getGreatestCommonDivisor(nums.length, k); i++) {
            int targetIndex = (i + k) % nums.length;
            while (targetIndex != i) {
                swap(nums, i, targetIndex);
                targetIndex = (targetIndex + k) % nums.length;
            }
        }
    }

    private int getGreatestCommonDivisor(int a, int b) {
        if (b == 0) {
            return a;
        }

        return getGreatestCommonDivisor(b, a % b);
    }

    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
}

该方法完全是在草稿纸上找规律找出来的。

Reverse

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
class Solution {
    public void rotate(int[] nums, int k) {
        k %= nums.length;
        if (k == 0) {
            return;
        }

        // 输入: nums = [1, 2, 3, 4, 5, 6, 7], k = 3 输出: [5, 6, 7, 1, 2, 3, 4]

        reverse(nums, 0, nums.length - 1);
        reverse(nums, 0, k - 1);
        reverse(nums, k, nums.length - 1);
    }

    private void reverse(int[] nums, int i, int j) {
        while (i < j) {
            swap(nums, i++, j--);
        }
    }

    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
}

References

189. Rotate Array