LeetCode 186. Reverse Words in a String II

Problem description:

Given an input string , reverse the string word by word. 

Example:

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

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

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：

分为两步解决此问题，第一不是单词的颠倒，第二步是单词内的颠倒。

时间复杂度：O(n), 空间复杂度O(1)

class Solution {
    public void reverseWords(char[] str) {
        int i = 0, j = str.length - 1;
        while(i < j) {
            swap(str, i++, j--);
        }
        for(i = 0; i < str.length; i++) {
            if(str[i] == ' ') continue;
            j = i;
            while(j < str.length) {
                if(str[j] == ' ') {
                    break;
                }
                j++;
            }
            int s = i, t = j - 1;
            while(s < t) {
                swap(str, s++, t--);
            }
            i = j;
        }
        
    }
    private void swap(char[] str, int i, int j) {
        char tmp = str[i];
        str[i] = str[j];
        str[j] = tmp;
    }
}