leetcode.500.Keyboard Row

Description

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

sln

1. 创建一个数字，记录26个字符分别属于哪一行（一个由0，1，2组成的数组）
2. 遍历每个单词，可以用O(1)的时间确定字母属于哪一行，那么可以用O(m)的时间确定整个单词是否可以用键盘的其中一行打出来，其中m为字符串长度
3. 用O(n * m)的时间可以完成整个任务，c++实现如下

class Solution {public:    vector<string> findWords(vector<string>& words) {        vector<string> ret;        int belongTo[] = {1, 2, 2, 1, 0, 1, 1, 1, 0, 1, 1, 1, 2, 2, 0, 0, 0, 0, 1, 0, 0, 2, 0, 2, 0, 2};        for (vector<string>::iterator it = words.begin(); it != words.end(); it++) {            string word = *it;            int group = -1;            bool flag = true;            for (int i = 0; i < word.length(); i++) {                int cgroup = belongTo[toLower(word[i]) - 'a'];                if (group != -1 && group != cgroup) {                    flag = false;                    break;                } else {                    group = cgroup;                }            }            if (flag) {                ret.push_back(word);            }        }        return ret;    }private:    char toLower(char a) {        if (a >= 'A' && a <= 'Z') {            return 'a' + (a - 'A');        }        return a;    }};