[LeetCode] 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".

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.

Solution:

class Solution {
public:
    void reverseWords(string &s) {
        int len = s.length(), start = 0, curLen = 0;
        
        string ans = "", tmp = "";
        bool isWord = false, notStartEmpty = false;
        for(int i = len - 1;i >= 0;i--)
        {
            if(s[i] == ' ')
            {
                if(isWord)
                {
                    isWord = false;
                    ans += s.substr(start - curLen + 1, curLen);
                    curLen = 0;
                }
                if(notStartEmpty)
                    tmp += s[i];
            }
            else
            {
                if(isWord)
                {
                    curLen++;
                }
                else
                {
                    isWord = true;
                    notStartEmpty = true;
                    if(tmp.length() > 0)
                     {
                        ans += " ";
                        tmp = "";
                    }
                    start = i;
                    curLen = 1;
                }
            }
        }
        if(curLen != 0)
            ans += s.substr(start - curLen + 1, curLen);
        s = ans;
    }
};