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Reverse String⚓︎

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Description⚓︎

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 <= 10^5
  • s[i] is a printable ascii character.

Solution⚓︎

Double Pointer⚓︎

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class Solution {
public:
    void reverseString(vector<char>& s) {
        for (int i = 0; i < s.size() / 2; i++)
            swap(s[i], s[s.size() - i - 1]);
    }
};

Another way of writing:

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class Solution {
public:
    void reverseString(vector<char>& s) {
        for (int i = 0, j = s.size() - 1; i < s.size() / 2; i++, j--) {
            // swap(s[i], s[j]);
            s[i] ^= s[j];
            s[j] ^= s[i];
            s[i] ^= s[j];
        }
    }
};
  • Time complexity: \(O(n)\);
  • Space complexity: \(O(1)\).