Leetcode Reverse Words in a String II

Given an input string, reverse the string word by word. A word is defined as a sequence of non-space characters.

The input string does not contain leading or trailing spaces and the words are always separated by a single space.

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

Could you do it in-place without allocating extra space?

Related problem: Rotate Array

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解题思路：

和Leetcode Rotate Array 思路一样。

（1）reverse the whole array

（2）reverse each subarray seperated by ' '

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Java code:

public class Solution {
    public void reverseWords(char[] s) {
        reverse(s, 0, s.length-1);
        int start = 0;
        for(int i = 0; i< s.length; i++){
            if(s[i] == ' '){
                reverse(s, start, i-1);
                start = i+1;
            }
        }
        reverse(s, start, s.length-1); 
    }
    
    public void reverse(char[] s, int l, int r){
        while(l < r){
            char temp = s[l];
            s[l] = s[r];
            s[r] = temp;
            l++;
            r--;
        }
    }
}

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Reference:

1. http://www.cnblogs.com/EdwardLiu/p/4306561.html

2. https://leetcode.com/discuss/24227/my-java-solution-with-explanation