151. Reverse Words in a String

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.

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1.方法一

class Solution {public:void reverseWords(string &s) {stringstream ss(s);ss>>s;string tmp;while(ss>>tmp){s=tmp+" "+s;}if(s[0]==' ') s="";}};

2.方法二

class Solution {public:void reverseWords(string &s) {int len=s.size();int i=0,j=0,k=0;int wordNum=0;while(true){while(i<len&&s[i]==' ') i++;if(i==len) break;if(wordNum) s[j++]=' ';k=j;while(i<len&&s[i]!=' '){s[j]=s[i];j++;i++;}reverseWord(s,k,j-1);wordNum++;}s.resize(j);reverseWord(s,0,j-1);}private:void reverseWord(string &s,int i,int j){while(i<j){swap(s[i++],s[j--]);}}};