ReverseString.java

/*
Write a function that reverses a string. The input string is given as an array of characters char[].

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

You may assume all the characters consist of printable ascii characters.

Example 1:
Input: ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]

Example 2:
Input: ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]
*/

class Solution {
    public void reverseString(char[] s) {
        if(s != null) {
            int i = 0;
            int j = s.length - 1;
            while(i < j) {
                swap(s, i, j);
                i ++;
                j --;
            }
        }
    }
    
    public void swap(char[] c, int i, int j) {
        char temp = c[i];
        c[i] = c[j];
        c[j] = temp;
    }
}