(字符串 数组 递归 双指针) leetcode 344. Reverse String

Write a function that reverses a string. The input string is given as an array of characters char[].

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

You may assume all the characters consist of printable ascii characters.

Example 1:

Input: ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]

Example 2:

Input: ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]

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1）
这个是水题，不过我打算用递归来解决它
C++代码：

class Solution {
public:
    void reverseString(vector<char>& s) {
        helper(s,0,s.size()-1);
    }
    void helper(vector<char>& s,int start,int end){
        if(start >= end){
            return;
        }
        char tmp = s[start];
        s[start] = s[end];
        s[end] = tmp;
        helper(s,start+1,end-1);  //是两端往中心靠的递归
    }
};

 2）

这个可以用双指针。

C++代码：

class Solution {
public:
    void reverseString(vector<char>& s) {
        int i = 0,j = s.size() - 1;
        while(i < j){
            swap(s[i],s[j]);
            i++;
            j--;
        }
    }
};