题目描述：

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.

American keyboard

Example 1:

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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.

判断每个字母在键盘上位于哪一行，可以用Hash表来保存每个字母所对应的行，也可以每次都搜索一次，因为数据量都很小所以性能差距很小。

Hash表：

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class Solution {
    vector<int> keymap = {2,3,3,2,1,2,2,2,1,2,2,2,3,3,1,1,1,1,2,1,1,3,1,3,1,3};
public:
    vector<string> findWords(vector<string>& words) {
        vector<string> ans;
        for (auto str : words) {
            int row = keymap[tolower(str[0]) - 'a'], i;
            for (i = 1; i < str.length(); i++) {
                if (keymap[tolower(str[i]) - 'a'] != row) break;
            }
            if (i == str.length()) ans.push_back(str);
        }
        return ans;
    }
};

搜索：

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class Solution {
    vector<string> keyboard = {"qwertyuiop", "asdfghjkl", "zxcvbnm"};
public:
    vector<string> findWords(vector<string>& words) {
        vector<string> ans;
        for (auto str : words) {
            int row = findRow(str[0]), i;
            for (i = 1; i < str.length(); i++) {
                if (findRow(str[i]) != row) break;
            }
            if (i == str.length()) ans.push_back(str);
        }
        return ans;
    }
    
    int findRow(char c) {
        c = tolower(c);
        for (int i = 0; i < keyboard.size(); i++) {
            if (keyboard[i].find(c) != string::npos) 
                return i;
        }
        return -1;
    }
};