Leetcode 500 Solution

class Solution {
public:
    vector<string> findWords(vector<string>& words) {
        unordered_set<char> row1 {'q', 'w', 'e', 'r', 't', 'y','u', 'i', 'o', 'p'};
        unordered_set<char> row2 {'a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l'};
        unordered_set<char> row3 {'z', 'x', 'c', 'v', 'b' ,'n', 'm'};

        vector<string> res;
        for (auto word : words)
        {
            bool valid = true;
            int row = 0;
            for (auto ch : word)
            {
                int next_row = 0;
                if (row1.find(tolower(ch)) != row1.end())
                    next_row = 1;
                else if (row2.find(tolower(ch)) != row2.end())
                    next_row = 2;
                else if (row3.find(tolower(ch)) != row3.end())
                    next_row = 3;

                if (row != 0 && row != next_row)
                {
                    valid = false;
                    break;
                }

                row = next_row;
            }

            if (valid)
                res.push_back(word);
        }

        return res;
    }
};