Write a function that takes a string as input and returns the string reversed.
Example:
Given s = "hello", return "olleh".
反转字符串,逼我不用 reverse
class Solution { public: string reverseString(string s) { int n = s.length(); int l = 0, r = n - 1; while(l < r) { swap(s[l++],s[r--]); } return s; } };