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 = 0;
        
        while (i < s.length()) {
            int j = i;
            while (j < s.length() && s[j] != ' ') {
                ++j;
            }
            
            reverseSelf(s, i, j - 1);
            
            i = j + 1;
        }
        
        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 = 0;
    for(int j = 0; j < s1.length; j++)
    {
        if(s1[j] == ' ')
        {
            reverse(s1, i, j - 1);
            i = j + 1;
        }
    }
    reverse(s1, i, s1.length - 1);
    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 = 0; 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 - 1;
            }
        }
        
        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