Given a List of words, return the words that can be typed using letters ofalphabeton 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.

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Hash Table

public class Solution {
    public String[] findWords(String[] words) {
       List<String> result = new ArrayList<String>();

        Map<Character,Integer> charMap = new HashMap<Character, Integer>();
        String[] keyboard = {"qwertyuiop","asdfghjkl","zxcvbnm"};
        for(int i=0;i<keyboard.length;i++){
            String key = keyboard[i];
            for(char c : key.toCharArray()){
                charMap.put(c, i);
            }
        }

        for (int i = 0; i < words.length; i++) {
            String word = words[i];
            int index = charMap.get(word.toLowerCase().charAt(0));
            for(int j=1;j<word.length();j++){
                if(charMap.get(word.toLowerCase().charAt(j)) != index){
                    index = -1;
                    break;
                }
            }
            if(index != -1){
                result.add(word);
            }
        }

        return result.toArray(new String[0]);
    }
}