Problem : Easy

LeetCode: Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory.

Thought

• This an easy problem if using two pointers (indexing);
• One pointer from the start of the string ( left) , One from the end of the string (right) , both traversing to the middle and swapping the char along the way.
• The key point will be when do we stop swapping the front element with the back element. Either using while loop, condition will be while (left <right), here doesn’t have to consider left == right because when they meet, there is no need to swap. Or using for loop, condition will be (int i< length/2-1).

Solution: Java

class Solution {
    public void reverseString(char[] s) {
        int l = 0;
        int r = s.length-1;
        for(int i=0; i<s.length/2 ; i++){
            char temp = s[l];
            s[l] = s[r];
            s[r] = temp;
            l++;
            r--;
        }
    }
}

For more instructions head over to the LeetCode.