From 6e3cf576e532b0c139c30960508e70fc7de30ae6 Mon Sep 17 00:00:00 2001
From: SquidSpirit <squid@squidspirit.com>
Date: Thu, 20 Feb 2025 22:54:00 +0800
Subject: [PATCH] feat: 17_letter_combinations_of_a_phone_number

---
 .../main.cpp                                  | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 17_letter_combinations_of_a_phone_number/main.cpp

diff --git a/17_letter_combinations_of_a_phone_number/main.cpp b/17_letter_combinations_of_a_phone_number/main.cpp
new file mode 100644
index 0000000..ac10304
--- /dev/null
+++ b/17_letter_combinations_of_a_phone_number/main.cpp
@@ -0,0 +1,43 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+   public:
+    unordered_map<char, unordered_set<string>> charmap = {
+        {'2', {"a", "b", "c"}},
+        {'3', {"d", "e", "f"}},
+        {'4', {"g", "h", "i"}},
+        {'5', {"j", "k", "l"}},
+        {'6', {"m", "n", "o"}},
+        {'7', {"p", "q", "r", "s"}},
+        {'8', {"t", "u", "v"}},
+        {'9', {"w", "x", "y", "z"}},
+    };
+
+    unordered_set<string> combineTwo(const unordered_set<string> &a, const unordered_set<string> &b) {
+        unordered_set<string> result;
+
+        for (auto first : a) {
+            for (auto second : b) {
+                result.insert(first + second);
+            }
+        }
+
+        return result;
+    }
+
+    vector<string> letterCombinations(string digits) {
+        if (digits.length() == 0) return {};
+
+        unordered_set<string> resultSet = charmap[digits[0]];
+
+        for (int i = 1; i < digits.length(); i++) {
+            resultSet = combineTwo(resultSet, charmap[digits[i]]);
+        }
+
+        vector<string> result;
+        for (auto s : resultSet) result.emplace_back(s);
+
+        return result;
+    }
+};