旋转数组

   

Rotate an array of n elements to the right by k steps.

For example, with n = 7 and k = 3, the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4].

大致的意思是数组向右旋转Ｋ次

   

解法1: 内存占用少, 但是时间上效率低点,

public class Solution {
    public void rotate(int[] nums, int k) {
        int n = nums.length;
        k = k % n;
        if(n == 1 || k <= 0)
        return;
        if(k == n) {
            reverse(nums, 0, n-1); 
        } else {
            reverse(nums, 0, n-k-1); 
            reverse(nums, n-k, n-1);
            reverse(nums, 0, n-1);
        }
    }
    
    private void reverse(int[] nums, int start, int end) {
        for(int i = start , j = end; i != j;) {
            int tmp = nums[i];
            nums[i] = nums[j];
            nums[j] = tmp;
            if(i+1 == j) {
                break;
            }
            i++;
            j--;
        }
    }
}

解法2:内存空间占用会大点，但是时间上效率高点

public class Solution {
    public void rotate(int[] nums, int k) {
        int n = nums.length;
        k = k % n;
        if(n == 1 || k <= 0)
        return;
        int[] tmp = new int[n];
        System.arraycopy(nums, n-k,tmp,0,k);
        System.arraycopy(nums, 0,tmp,k,n-k);
        System.arraycopy(tmp, 0,nums,0,n);
    }
}