leetcode 344. Reverse String

Write a function that reverses a string. The input string is given as an array of characters char[].

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

You may assume all the characters consist of printable ascii characters.

Example 1:

Input: [“h”,“e”,“l”,“l”,“o”]
Output: [“o”,“l”,“l”,“e”,“h”]

method 1

雙指針法，使用兩根相反的指針

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

method 2

使用分治法

class Solution {
  public void helper(char[] s, int left, int right) {
    if (left >= right) return;
    char tmp = s[left];
    s[left++] = s[right];
    s[right--] = tmp;
    helper(s, left, right);
  }

  public void reverseString(char[] s) {
    helper(s, 0, s.length - 1);
  }
}

summary

1. 雙指針法
2. 分治法