1. 题目

在老式手机上，用户通过数字键盘输入，手机将提供与这些数字相匹配的单词列表。
每个数字映射到0至4个字母。给定一个数字序列，实现一个算法来返回匹配单词的列表。
你会得到一张含有有效单词的列表。映射如下图所示：

示例 1:
输入: num = "8733", words = ["tree", "used"]
输出: ["tree", "used"]示例 2:
输入: num = "2", words = ["a", "b", "c", "d"]
输出: ["a", "b", "c"]提示：
num.length <= 1000
words.length <= 500
words[i].length == num.length
num中不会出现 0, 1 这两个数字

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/t9-lcci
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

2. 解题

类似题目：LeetCode 17. 电话号码的字母组合（回溯）

class Solution {
public:vector<string> getValidT9Words(string num, vector<string>& words) {string key[10] = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};vector<string> ans;int i;bool ok;for(auto& w : words){ok = true;for(i = 0; i < w.size(); ++i){if(key[num[i]-'0'].find(w[i]) == string::npos){ok = false;break;}}if(ok)ans.push_back(w);}return ans;}
};

36 ms 12.2 MB

• 或者比较数字是否相等

class Solution {
public:vector<string> getValidT9Words(string num, vector<string>& words) {char ch[26] = {'2', '2', '2', '3', '3', '3', '4', '4', '4','5', '5', '5', '6', '6', '6', '7', '7', '7', '7', '8', '8', '8', '9', '9', '9', '9'};vector<string> ans;int i;bool ok;for(auto& w : words){ok = true;for(i = 0; i < w.size(); ++i){if(num[i] != ch[w[i]-'a']){ok = false;break;}}if(ok)ans.push_back(w);}return ans;}
};

28 ms 12 MB