LeetCode Keyboard Row

原题链接在这里：https://leetcode.com/problems/keyboard-row/#/description

题目：

Given a List of words, return the words that can be typed using letters of alphabet on only one row's of American keyboard like the image below.

Example 1:

Input: ["Hello", "Alaska", "Dad", "Peace"]
Output: ["Alaska", "Dad"]

Note:

1. You may use one character in the keyboard more than once.
2. You may assume the input string will only contain letters of alphabet.

题解：

把在同row的char标记成同index存在HashMap<Character, Integer> hm中. 

然后判定word中的每一个char是否有相同的index.

Time Complexity: O(n), n是words中每个word的char总和.

Space: O(1). hm size, regardless res size.

AC Java:

public class Solution {
    public String[] findWords(String[] words) {
        if(words == null || words.length == 0){
            return words;
        }
        
        String [] keyboard = {"qwertyuiop", "asdfghjkl", "zxcvbnm"};
        HashMap<Character, Integer> hm = new HashMap<Character, Integer>();
        for(int i = 0; i<keyboard.length; i++){
            for(char c : keyboard[i].toCharArray()){
                hm.put(c, i);
            }
        }
        
        List<String> res = new ArrayList<String>();
        for(String word : words){
            if(word == null || word.length() == 0){
                continue;
            }
            int ind = hm.get(word.toLowerCase().charAt(0));
            for(char c : word.toLowerCase().toCharArray()){
                if(ind != hm.get(c)){
                    ind = -1;
                }
            }
            if(ind != -1){
                res.add(word);
            }
        }
        
        return res.toArray(new String[0]);
    }
}