字符串反转

输入一个 abcd, 输出一个 dcba

public String solve (String str) {
    // write code here
    return return new StringBuffer(str).reverse().toString();
}

或者遍历到 StringBuffer

public String solve (String str) {
    // write code here
    if (str.length() == 0) {
        return "";
    }
    char c[] = str.toCharArray();
    StringBuffer s = new StringBuffer();
    for (int i = c.length-1; i >= 0; i--) {
        s.append(c[i]);
    }
    return s.toString();
}