557. Reverse Words in a String III【easy】

557. Reverse Words in a String III【easy】

Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example 1:

Input: "Let's take LeetCode contest"
Output: "s'teL ekat edoCteeL tsetnoc"

Note: In the string, each word is separated by single space and there will not be any extra space in the string.

解法一：

 class Solution {
 public:
     void reverseSelf(string & s, int start, int end)
     {
         while (start <= end) {
             char c = s[start];
             s[start] = s[end];
             s[end] = c;
             ++start;
             --end;
         }
     }

     string reverseWords(string s) {
         int i = ;

         while (i < s.length()) {
             int j = i;
             while (j < s.length() && s[j] != ' ') {
                 ++j;
             }

             reverseSelf(s, i, j - );

             i = j + ;
         }

         return s;
     }
 };

无他，注意下标边界尔。

解法二：

 public String reverseWords(String s)
 {
     char[] s1 = s.toCharArray();
     int i = ;
     for(int j = ; j < s1.length; j++)
     {
         if(s1[j] == ' ')
         {
             reverse(s1, i, j - );
             i = j + ;
         }
     }
     reverse(s1, i, s1.length - );
     return new String(s1);
 }

 public void reverse(char[] s, int l, int r)
 {
     while(l < r)
     {
         char temp = s[l];
         s[l] = s[r];
         s[r] = temp;
         l++; r--;
     }
 }

参考@sooryaprasanna 的代码

Step 1. Convert the string to char[] array
Step 2. Whenever I encounter a space ' ' , I call the reverse function ( just to keep the code clean )
Step 3. Repeat till the end!

解法三：

 class Solution {
 public:
     string reverseWords(string s) {
         for (int i = ; i < s.length(); i++) {
             if (s[i] != ' ') {   // when i is a non-space
                 int j = i;
                 for (; j < s.length() && s[j] != ' '; j++) { } // move j to the next space
                 reverse(s.begin() + i, s.begin() + j);
                 i = j - ;
             }
         }

         return s;
     }
 };

参考@alexander 的代码。

补充一下reverse函数：

reverse函数可以反转一个容器中的内容，包含在<algorithm>库中。

1、函数原型

reverse函数等同于下面的代码：

 template <class BidirectionalIterator> void reverse (BidirectionalIterator first, BidirectionalIterator last)
 {
      while ((first!=last)&&(first!=--last))
      {
           std::iter_swap (first,last);
           ++first;
      }
 }

reverse函数使用iter_swap来交换两个元素。

2、参数：first、last

first和last是双向迭代器类型，reverse函数反转的范围是[first,last)，所以包括first指向的元素，不包括last指向的元素。

3、返回值

reverse函数没有返回值。

参考自：http://blog.csdn.net/u012877472/article/details/49557077