LeetCode 541. Reverse String II (反转字符串 II)

Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there are less than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and left the other as original.

Example:

Input: s = "abcdefg", k = 2
Output: "bacdfeg"

Restrictions:

1. The string consists of lower English letters only.
2. Length of the given string and k will in the range [1, 10000]

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题目标签：String

　　今天登陆突然发现LeetCode 有中文版本了- -，再也不用纠结于 如何翻译题目名字了。

 

　　题目给了我们一个string s 和 int k，让我们每次在2k 个 chars 里只反转 k 个chars。

　　利用Reverse String 里的 two pointers 来反转k 个chars，每一次增加 i by 2*k 就可以了。

　　具体请看code。

 

 

 

Java Solution:

Runtime beats 67.31%

完成日期：04/07/2018

关键词：two pointers

关键点：swap left and right chars

 class Solution
 {
     public String reverseStr(String s, int k)
     {
         char [] c_arr  = s.toCharArray();

         for(int i=0; i<c_arr.length; i=i+2*k)
         {
             int left = i;
             int right = Math.min(i + k - 1, c_arr.length - 1); 

             while(left < right)
             {
                 // swap char
                 char temp = c_arr[left];
                 c_arr[left] = c_arr[right];
                 c_arr[right] = temp;

                 left++;
                 right--;
             }

         }

         return new String(c_arr);
     }
 }

参考资料：n/a

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