Reverse String

Easytwo-pointersstring

Category: Fundamentals

Companies that ask this question:

AmazonMicrosoftGoogle

Approach

Reverse String

Approach

Use two pointers technique to swap characters from both ends moving toward the center.

Algorithm

Initialize left pointer at start (0) and right pointer at end (n-1)
While left < right:
- Swap characters at left and right positions
- Move left pointer forward
- Move right pointer backward
Process completes when pointers meet in the middle

Complexity

Time: O(n) - single pass through half the array
Space: O(1) - in-place modification, no extra space

Key Insights

Two-pointer technique is optimal for in-place reversal
Only need to process half the array
Works for both even and odd length arrays

Solution

java

1class Solution {
2    public void reverseString(char[] s) {
3        int left = 0, right = s.length - 1;
4        
5        while (left < right) {
6            char temp = s[left];
7            s[left] = s[right];
8            s[right] = temp;
9            left++;
10            right--;
11        }
12    }
13}

Loading visualizer...