189. Rotate Array

Problem:

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?

思路：

Solution (C++):

void rotate(vector<int>& nums, int k) {
    int n = nums.size();
    k %= n;
    vector<int> tmp(k, 0);
    for (int i = 0; i < k; ++i) {
        tmp[i] = nums[i+n-k];
    }
    for (int i = n-1; i >= k; --i) {
        nums[i] = nums[i-k];
    }
    for (int i = 0; i < k; ++i) {
        nums[i] = tmp[i];
    }
}

性能：

Runtime: 12 ms  Memory Usage: 7.4 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB