344 Reverse String

344. Reverse String

1. Question

Write a function that takes a string as input and returns the string reversed.

Example: Given s = "hello", return "olleh".

2. Implementation

(1) Two Pointers

class Solution {
    public String reverseString(String s) {
        int start = 0, end = s.length() - 1;
        char[] letters = s.toCharArray();

        while (start < end) {
            char temp = letters[start];
            letters[start] = letters[end];
            letters[end] = temp;
            ++start;
            --end;
        }
        return new String(letters);
    }
}

3. Time & Space Complexity

Two Pointers: 时间复杂度O(n), 空间复杂度O(1)