LeetCode541. Reverse String II

一、题目

541. Reverse String II

Given a string s and an integer k, reverse the first k characters for every 2k characters counting from the start of the string.

If there are fewer than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and leave the other as original.

Example 1:

Input: s = “abcdefg”, k = 2
Output: “bacdfeg”
Example 2:

Input: s = “abcd”, k = 2
Output: “bacd”

Constraints:

1 <= s.length <= 104
s consists of only lowercase English letters.
1 <= k <= 104

二、题解

class Solution {
public:
    string reverseStr(string s, int k) {
        int n = s.length();
        //循环处理2k个单位
        for(int i = 0;i < n;i += 2 * k){
            if(i + k <= n){
                reverse(s.begin() + i,s.begin() + i + k);
            }
            else reverse(s.begin() + i,s.end());
        }
        return s;
    }
};