Reverse String

Approach

1. Initialize two pointers:
   • l at the start of the array
   • r at the end of the array
2. While l < r, swap s[l] and s[r].
3. Move both pointers inward (l++, r--) and continue.
4. Stop when pointers meet or cross; at that point the array is fully reversed.

Implementation

export function reverseString(s: string[]): void {
    function swap(arr: string[], idx1: number, idx2: number): void {
        [arr[idx1], arr[idx2]] = [arr[idx2], arr[idx1]];
    }
 
    let l = 0;
    let r = s.length - 1;
 
    while (l < r) {
        swap(s, l, r);
 
        l++;
        r--;
    }
}

Complexity

• Time O(n): Each element is visited at most once as pointers move toward the center.
• Space O(1): Reversal is done in-place with constant extra memory.