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"]
[code lang="java"]
class Solution {
    public void reverseString(char[] s) {
        
    }
}
[code]

Idea – 1

We swap the two ends and move inwards. Now we have n-2 characters to reverse, we do this repeatedly. Time complexity O(n), space complexity O(1). 
[code lang="java"]
class Solution {
    public void reverseString(char[] s) {
        if(s == null || s.length < 2)
        {
            return;
        }
        
        int i = 0, j = s.length-1;
        while(i < j)
        {
            swap(s, i++, j--);
        }
    }
    
    private void swap(char[] A, int i, int j)
    {
        char tmp = A[i];
        A[i] = A[j];
        A[j] = tmp;
    }
}
[code]

Runtime: 1 ms, faster than 100.00% of Java online submissions for Reverse String.Memory Usage: 47.4 MB, less than 64.05% of Java online submissions for Reverse String.

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