[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.　　

 

没什么多说的，去空格看似挺麻烦，一次遍历就能搞定。注意最后的空格要特殊处理。

 

class Solution {
public:
    void reverse(string &s, int low, int high) {
        char tmp;
        while(low < high) {
            tmp = s[low];
            s[low] = s[high];
            s[high] = tmp;
            low++;
            high--;
        }
    }
    
    void removeBlank(string &s) {
        if (s.length() == 0) {
            return;
        }
        int count = 0;
        bool flag = false;
        for (int i = 0; i <= s.length(); ++i) {
            if (s[i] == ' ' && !flag) {
                count++;
            } else if (s[i] == ' ' && flag) {
                flag = false;
                s[i-count] = s[i];
            } else if (s[i] != ' ') {
                flag = true;
                s[i-count] = s[i];
            }
        }
        int len = s.length() - count;
        if (s[len-1] == ' ') {
            s[len-1] = '\0';
            len--;
        }
        s.resize(len);
    }

    void reverseWords(string &s) {
        removeBlank(s);
        reverse(s,0,s.length()-1);
        int a = 0, b;
        for (int i=0; i<=s.length();++i){
            if(s[i]==' '||s[i]=='\0'){
                b = i-1;
                reverse(s,a,b);
                a = i+1;
            }
        }
        return;
    }
};