面试经典150题——Day6

一、题目

Given an integer array nums, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: nums = [1,2,3,4,5,6,7], 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: nums = [-1,-100,3,99], 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]

Constraints:

1 <= nums.length <= 105
-231 <= nums[i] <= 231 - 1
0 <= k <= 105

Follow up:

Try to come up with as many solutions as you can. There are at least three different ways to solve this problem.
Could you do it in-place with O(1) extra space?

题目来源：leetcode

二、题解

笨方法

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        vector<int> res;
        int len = nums.size();
        int step = 0;
        if(k < len) step = len - k;
        else step = len - k % len;
        for(int i = step;i < len;i++){
            res.push_back(nums[i]);
        }
        for(int i = 0;i < step;i++){
            res.push_back(nums[i]);
        }
        for(int i = 0;i < len;i++){
            nums[i] = res[i];
        }
    }
};

更好的做法

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        int n = nums.size();
        vector<int> newArr(n);
        for (int i = 0; i < n; ++i) {
            newArr[(i + k) % n] = nums[i];
        }
        nums.assign(newArr.begin(), newArr.end());
    }
};