class Solution {
public:
    void swap(char &ch1, char &ch2){
        
    }
    /**
     * 反转字符串
     * @param str string字符串 
     * @return string字符串
     */
    string solve(string str) {
        // write code here
        char ch;
        int sz = str.size();
        for(int i=0; i<sz-1-i; i++){
            ch = str[i];
            str[i] = str[sz-1-i];
            str[sz-1-i] = ch;
        }
        return str;
    }
};