LeetCode Reverse Words in a String II

原题链接在这里：https://leetcode.com/problems/reverse-words-in-a-string-ii/

题目：

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?

题解：

input变成 char array.

先reverse 全部 char array. 从头往后走，遇到空格或者array尾部，就reverse中间的单词.

Note: Do NOT forget i == n, reverse.

Time Compelxity: O(s.length()). Space: O(1).

AC Java:

 public class Solution {
     public void reverseWords(char[] s) {
         if(s == null || s.length == 0){
             return;
         }
         reverse(s, 0, s.length-1);

         int lo = 0;
         for(int i = 1; i<=s.length; i++){
             if(i == s.length || s[i] == ' '){
                 reverse(s, lo, i-1);
                 lo = i+1;
             }
         }
     }

     private void reverse(char [] s, int i, int j){
         while(i < j){
             swap(s, i++, j--);
         }
     }

     private void swap(char [] s, int i , int j){
         char temp = s[i];
         s[i] = s[j];
         s[j] = temp;
     }
 }

类似Reverse Words in a String.

跟上Reverse Words in a String III, Rotate Array.