500. Keyboard Row(判断字符串字符是否在一行)

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.

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public class Solution {    public String[] findWords(String[] words) {        String[] strs = {"QWERTYUIOP","ASDFGHJKL","ZXCVBNM"};        Map<Character, Integer> map = new HashMap<>();        for(int i = 0; i<strs.length; i++){            for(char c: strs[i].toCharArray()){                map.put(c, i);//put <char, rowIndex> pair into the map            }        }        List<String> res = new LinkedList<>();        for(String w: words){            if(w.equals("")) continue;            int index = map.get(w.toUpperCase().charAt(0));            for(char c: w.toUpperCase().toCharArray()){                if(map.get(c)!=index){                    index = -1; //don't need a boolean flag.                     break;                }            }            if(index!=-1) res.add(w);//if index != -1, this is a valid string        }        return res.toArray(new String[0]);    }}