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Question

Formatted question description: https://leetcode.ca/all/344.html

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.

Algorithm

Go from both ends to the middle while swapping characters on both sides.

Code

• Java
• C++
• Python
• Go
• Javascript
• RenderScript

• 
  public class Reverse_String {
  
      class Solution {
          public void reverseString(char[] s) {
  
              int l = 0;
              int r = s.length - 1;
  
              while (l < r) {
                  char tmp = s[l];
                  s[l] = s[r];
                  s[r] = tmp;
                  l++;
                  r--;
              }
          }
      }
  
      class Solution_cheat {
          public String reverseString(String input) {
  
              StringBuilder s = new StringBuilder(input);
              s.reverse();
  
              return s.toString();
          }
      }
  }
  
  ############
  
  class Solution {
      public void reverseString(char[] s) {
          for (int i = 0, j = s.length - 1; i < j; ++i, --j) {
              char t = s[i];
              s[i] = s[j];
              s[j] = t;
          }
      }
  }
  

• // OJ: https://leetcode.com/problems/reverse-string/
  // Time: O(N)
  // Space: O(1)
  class Solution {
  public:
      void reverseString(vector<char>& s) {
          int i = 0, j = s.size() - 1;
          while (i < j) swap(s[i++], s[j--]);
      }
  };
  

• class Solution:
      def reverseString(self, s: List[str]) -> None:
          """
          Do not return anything, modify s in-place instead.
          """
          s[:] = s[::-1]
  
  ############
  
  class Solution(object):
    def reverseString(self, s):
      """
      :type s: str
      :rtype: str
      """
      return s[::-1]
  
  

• func reverseString(s []byte) {
  	for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
  		s[i], s[j] = s[j], s[i]
  	}
  }
  

• /**
   * @param {character[]} s
   * @return {void} Do not return anything, modify s in-place instead.
   */
  var reverseString = function (s) {
      for (let i = 0, j = s.length - 1; i < j; ++i, --j) {
          [s[i], s[j]] = [s[j], s[i]];
      }
  };
  
  

• impl Solution {
      pub fn reverse_string(s: &mut Vec<char>) {
          let n = s.len();
          let mut l = 0;
          let mut r = n - 1;
          while l < r {
              s.swap(l, r);
              l += 1;
              r -= 1;
          }
      }
  }
  
  

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