LeetCode Reverse Words in a String III

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

题目：

Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example 1:

Input: "Let's take LeetCode contest"
Output: "s'teL ekat edoCteeL tsetnoc"

Note: In the string, each word is separated by single space and there will not be any extra space in the string.

题解：

与Reverse String II类似。原题中提到没有多余的space, 所以降低了难度.

遇到空格就把之前标记的部分reverse. 

Note: 最后一次reverse别忘了.

Time Complexity: O(n), n = s.length().

Space: O(n), char array.

AC Java:

class Solution {
    public String reverseWords(String s) {
        if(s == null || s.length() == 0){
            return s;
        }
        
        int len = s.length();
        char [] charArr = s.toCharArray();
        
        int lo = 0;
        for(int i = 0; i<=len; i++){
            if(i==len || charArr[i]==' '){
                reverse(charArr, lo, i-1);
                lo = i+1;
            }
        }
        
        return new String(charArr);
    }
    
    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;
    }
}