LeetCode — 344. Reverse String

Reversing a String with a Two-Pointer Approach

Reversing a string is a common problem in programming. It can be efficiently solved by using a simple two-pointer approach. This method is advantageous because it modifies the string in place without the need for additional memory for a new string.

Process

1. Initialize Two Pointers: We start by initializing two pointers, left at the start of the array and right at the end.
2. Swap Elements: We then enter a loop where we swap the elements at the left and right pointers.
3. Move Pointers: After each swap, we move the left pointer one step forward and the right pointer one step backward.
4. Loop Condition: This process continues until the left pointer is greater than or equal to the right pointer, indicating that the entire array has been reversed.

Time and Space Complexity

Time Complexity: The time complexity of this function is O(n), where n is the length of the string. Each element is swapped only once.
Space Complexity: The space complexity is O(1), as the reversal is done in place with no need for extra space.

JavaScript version

/**
 * @param {character[]} s
 * @return {void} Do not return anything, modify s in-place instead.
 */
var reverseString = function (s) {
    let left = 0, right = s.length - 1;

    while (left < right) {
        let temp = s[left];
        s[left] = s[right];
        s[right] = temp;

        left++;
        right--;
    }
};

Java version

class Solution {
    public void reverseString(char[] s) {
        int left = 0;
        int right = s.length - 1;

        while (left < right) {
            char temp = s[left];
            s[left] = s[right];
            s[right] = temp;

            left++;
            right--;
        }
    }
}