[LeetCode] Reverse Words in a String II

Problem

Reverse Words in a String II
Given an input string , reverse the string word by word.

Example

Input: ["t","h","e"," ","s","k","y"," ","i","s"," ","b","l","u","e"]
Output: ["b","l","u","e"," ","i","s"," ","s","k","y"," ","t","h","e"]

Note

A word is defined as a sequence of non-space characters.
The input string does not contain leading or trailing spaces.
The words are always separated by a single space.
Follow up: Could you do it in-place without allocating extra space?

Solution

class Solution {
    public void reverseWords(char[] str) {
        int start = 0, end = str.length-1;
        //reverse all chars
        reverse(str, start, end);
        for (int i = 0; i < str.length; i++) {
            //reverse all words back, except for the last one
            if (str[i] == ' ') {
                reverse(str, start, i-1);
                start = i+1;
            }
        }
        //reverse the last word back
        reverse(str, start, end);
    }
    private void reverse(char[] str, int i, int j) {
        while (i < j) {
            char temp = str[i];
            str[i] = str[j];
            str[j] = temp;
            i++;
            j--;
        }
    }
}