#53 Reverse Words in a String

题目描述：

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

For example,

Given s = "

the sky is blue

",

return "

blue is sky the

".

Have you met this question in a real interview? 

Yes

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.

题目思路：

这题我用了最直观的方法：先把word一个一个挑出来，放到一个stack中，然后把stack中的word一个一个pop出来组成string。这里写code注意小心处理最后一个word的情况就好。

Mycode（AC = 12ms）：

class Solution {
public:
/**
* @param s : A string
* @return : A string
*/
string reverseWords(string s) {
// write your code here
stack<string> words;

// select out each word in the string
// and put them into a stack
int l = 0, r = 0;
while (l < s.length()) {
while (l < s.length() && s[l] == ' ') {
l++;
}

if (l >= s.length()) break;

r = l;
while (r < s.length() && s[r] != ' ') {
r++;
}

string word = s.substr(l, r - l);
words.push(word);

l = r + 1;
}

// pop out word in the stack and
// get the final string
string ans = "";
while (!words.empty()) {
ans = ans + words.top() + " ";
words.pop();
}

return ans == ""? ans : ans.substr(0, ans.length() - 1);
}
};