0344. Reverse String

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.

Example 1:

Input: s = ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]

Example 2:

Input: s = ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]

Constraints:

• 1 <= s.length <= 105
• s[i] is a printable ascii character.

Analysis

Can be solved using simple two pointers trick.

• Time: $O(n)$
• Space: $O(1)$

Code

class Solution {
public:
    void reverseString(vector<char>& s) {
        for (int l = 0, r = s.size() - 1; l < r; l ++, r --) {
            char t = s[l];
            s[l] = s[r];
            s[r] = t;
        }
    }
};

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Last update: April 1, 2022