[LeetCode] Reverse String

Write a function that takes a string as input and returns the string reversed.

Example:
Given s = "hello", return "olleh".

题目要求反转一个字符串，利用双指针求解。

class Solution {
public:
    string reverseString(string s) {
        int left = 0, right = s.size() - 1;
        while (left <= right)
            swap(s[left++], s[right--]);
        return s;
    }
};
// 9 ms

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