344. Reverse String

Description of the Problem

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

Tags: String

Code(Rust)

impl Solution {
    pub fn reverse_string(s: &mut Vec<char>) {
        let (mut i, mut j) = (0, s.len() - 1);
        while( i < j){
            let c = s[i];
            s[i] = s[j];
            s[j] = c;
            i+=1; j-=1;
        }
    }
}

Code(Java)

class Solution {
    public void reverseString(char[] s) {
        int i = 0; int j = s.length - 1;
        while( i < j){
            char c = s[i];
            s[i] = s[j];
            s[j] = c;
            i++; j--;
        }
    }
}

Complexity

• n is the length of the string

Time complexity:

• \( T(n) = O(n/2) \)

Auxiliary Space:

• \( S(n) = O(1) \)