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 = 2Output: "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]
   1 class Solution { 2 public: 3     string reverseStr(string s, int k) { 4             int len = s.size(); 5         string s1 = ""; 6         if (len
          
           = 0; i--) 9             {10                 s1 += s[i];11             }12         }13         else14         {15             for (int i = 0; i < len; i = i + 2*k)16             {17               for(int j=(i+k-1>len?len-1:(i+k-1));j>=i;j--)18               {19                   s1+=s[j];20               }21               for(int j=i+k;j<((i+2*k)>len?len:(i+2*k));j++)22               {23                   s1+=s[j];24               }25             }26         }27         return s1;28     }29 };
          

   我的代码普遍有个特点，就是暴力，哎，什么时候才能学会取巧呢？下面的是比较好的算法。

   1 class Solution { 2     void reverse(string &s, int l, int r) 3     { 4         if (r > (s.length() - 1)) 5             r = s.length() - 1; 6         while (l < r) 7         { 8             swap(s[l], s[r]); 9             l++;10             r--;11         }12     }13 public:14     string reverseStr(string s, int k) {15 16         for (int i = 0; i