[LeetCode]151.Reverse Words in a String

题目

Given an input string, reverse the string word by word.

For example,
Given s = “the sky is blue”,
return “blue is sky the”.

Update (2015-02-12):
For C programmers: Try to solve it in-place in O(1) space.

click to show clarification.

Clarification:
What constitutes a word?
A sequence of non-space characters constitutes a word.
Could the input string contain leading or trailing spaces?
Yes. However, your reversed string should not contain leading or trailing spaces.
How about multiple spaces between two words?
Reduce them to a single space in the reversed string.

思路

两次反转法。这里注意单词之间的多个空格只留一个空格以及去掉前导0和后导0。

代码

/*---------------------------------------
*   日期：2015-05-05
*   作者：SJF0115
*   题目: 151.Reverse Words in a String
*   网址：https://leetcode.com/problems/reverse-words-in-a-string/
*   结果：AC
*   来源：LeetCode
*   博客：
-----------------------------------------*/
#include <iostream>
#include <vector>
using namespace std;

class Solution {
public:
    void reverseWords(string &s) {
        int size = s.size();
        if(size <= 0){
            return;
        }//if
        // 前导0
        int index = 0;
        while(s[index] == ‘ ‘){
            ++index;
        }//while
        int left = index;
        // 后导0
        index = size - 1;
        while(s[index] == ‘ ‘){
            --index;
        }//while
        int right = index;
        // 连续空格只保留一个
        for(int i = left;i <= right;){
            if(i > left && s[i-1] == ‘ ‘ && s[i] == ‘ ‘){
                s.erase(i-1,1);
                --right;
            }//if
            else{
                ++i;
            }
        }//for
        // 翻转
        int start = left,end = left;
        for(int i = left;i <= right+1;++i){
            if(i == right+1 || s[i] == ‘ ‘){
                Reverse(s,start,end-1);
                ++end;
                start = end;
            }//if
            else{
                ++end;
            }//else
        }//for
        // 整体翻转
        Reverse(s,left,right);
        s = s.substr(left,right - left + 1);
    }
private:
    void Reverse(string &str,int start,int end){
        for(int i = start,j = end;i < j;++i,--j){
            swap(str[i],str[j]);
        }//for
    }
};

int main() {
    Solution solution;
    //string str("   abc    cd     ef ");
    string str("  a   vvv  ");
    solution.reverseWords(str);
    cout<<str<<endl;
}

运行时间