/**
 * 反转字符串
 * @param str string字符串 
 * @return string字符串
 */
char* solve(char* str ) {
    // write code here
    int i, j;
    char tmp;
    int n = strlen(str);
    if(n == 0 || n == 1)
        return str;
    
    for(i = 0, j = n-1; i < j; i++, j--)
    {
        tmp = str[i];
        str[i] = str[j];
        str[j] = tmp;
    }
    return str;
}