541.Reverse String II(String-Easy)

Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there are less 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 left the other as original.

Example:

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

Restrictions:

• The string consists of lower English letters only.
• Length of the given string and k will in the range [1, 10000]

题目：根据k，反转字符串。

    /**
     * 0            k           2k          3k
     * |-----------|-----------|-----------|---
     * +--reverse--+           +--reverse--+
     */

每2k个字符，反转前面的k个字符。如果少于k个字符，反转所有字符。如果大于等于k个字符小于2k个字符，那么反转前面的k个字符，剩余的字符保留不动。

思路：使用reverse函数进行反转。代码依旧很简单。

Language : cpp

class Solution {
public:
    string reverseStr(string s, int k) {
        for(int i = 0; i < s.size(); i += 2*k){
            reverse(s.begin()+i, min(s.begin()+i+k, s.end()));
        }
        return s;
    }
};