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186. reverse words in a string ii Method Code Point

admin 11月 11, 2020 0

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?

Method

reverse the whole sentense
reverse each word
PS: remember to reverse the last word

Code

public class Solution {
    public void reverseWords(char[] s) {
        
        //1.reverse the whole array
        reverse(s, 0, s.length-1);      //way to reverse array
        //Collections.reverse(list); --> way to reverse list
        
        //2.reverse each word
        int start = 0;
        for(int i = 0; i < s.length; i++){
            if(s[i] == ' '){
                reverse(s, start, i-1);
                start = i + 1;
            }
        }
        //3.reverse the last word if there is one
        reverse(s, start, s.length - 1);
    }
    
    private void reverse(char[] s, int start, int end){
        while(start < end){
            char temp = s[start];
            s[start] = s[end];
            s[end] = temp;
            start++;
            end--;
        }
    }
}

Point

Collections.reverse(list) ==> not used in the question, but quite useful when sortin array