Problem

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

Example

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

Solution

1. Two-Pointer --3ms

public class Solution {
    public String reverseString(String s) {
        char[] str = s.toCharArray();
        int left = 0, right = str.length-1;
        while (left < right) {
            char temp = str[left];
            str[left] = str[right];
            str[right] = temp;
            left++;
            right--;
        }
        return new String(str);
    }
}

2. StringBuilder --5ms

public class Solution {
    public String reverseString(String s) {
        return  new StringBuilder(s).reverse().toString();
    }
}

3. Recursion --22ms

public class Solution {
    public String reverseString(String s) {
        int len = s.length();
        if (len <= 1) return s;
        String leftStr = s.substring(0, len / 2);
        String rightStr = s.substring(len / 2, len);
        return reverseString(rightStr) + reverseString(leftStr);
    }
}