From dab34e04adb41ffcef04570bdc8c2577ee1447eb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9=20Borba?= <andre.borbaaf2b@gmail.com>
Date: Sat, 19 Sep 2026 09:23:00 -0300
Subject: [PATCH] =?UTF-8?q?=F0=9F=9F=A1=20Port=20problem=2017=20(Letter=20?=
 =?UTF-8?q?Combinations=20of=20a=20Phone=20Number)=20from=20Swift=20to=20C?=
 =?UTF-8?q?++23?=
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Content-Type: text/plain; charset=UTF-8
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Replaces swift/17.swift with
solutions/0001-0100/0017-letter-combinations-of-a-phone-number/.
---
 .../README.md                                 | 11 +++++
 .../solution.cpp                              | 38 +++++++++++++++
 .../solution.hpp                              | 12 +++++
 .../test.cpp                                  | 10 ++++
 swift/17.swift                                | 48 -------------------
 5 files changed, 71 insertions(+), 48 deletions(-)
 create mode 100644 solutions/0001-0100/0017-letter-combinations-of-a-phone-number/README.md
 create mode 100644 solutions/0001-0100/0017-letter-combinations-of-a-phone-number/solution.cpp
 create mode 100644 solutions/0001-0100/0017-letter-combinations-of-a-phone-number/solution.hpp
 create mode 100644 solutions/0001-0100/0017-letter-combinations-of-a-phone-number/test.cpp
 delete mode 100644 swift/17.swift

diff --git a/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/README.md b/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/README.md
new file mode 100644
index 0000000..5ee21c7
--- /dev/null
+++ b/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/README.md
@@ -0,0 +1,11 @@
+# 17. Letter Combinations of a Phone Number
+
+[LeetCode problem 17](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)
+
+- **Difficulty**: Medium
+- **Tags**: hash-table, string, backtracking
+
+## Description
+
+Given a string of digits from `2` to `9`, return all possible letter
+combinations the digits could represent on a phone keypad, in any order.
diff --git a/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/solution.cpp b/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/solution.cpp
new file mode 100644
index 0000000..9b906f9
--- /dev/null
+++ b/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/solution.cpp
@@ -0,0 +1,38 @@
+#include "solution.hpp"
+
+#include <unordered_map>
+
+namespace leetcode::p0017 {
+
+std::vector<std::string> solve(const std::string& digits) {
+    if (digits.empty()) {
+        return {};
+    }
+
+    static const std::unordered_map<char, std::string> keypad{
+        {'2', "abc"},
+        {'3', "def"},
+        {'4', "ghi"},
+        {'5', "jkl"},
+        {'6', "mno"},
+        {'7', "pqrs"},
+        {'8', "tuv"},
+        {'9', "wxyz"},
+    };
+
+    std::vector<std::string> result{""};
+
+    for (char digit : digits) {
+        std::vector<std::string> next;
+        for (const auto& combination : result) {
+            for (char letter : keypad.at(digit)) {
+                next.push_back(combination + letter);
+            }
+        }
+        result = std::move(next);
+    }
+
+    return result;
+}
+
+} // namespace leetcode::p0017
diff --git a/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/solution.hpp b/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/solution.hpp
new file mode 100644
index 0000000..92fe440
--- /dev/null
+++ b/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/solution.hpp
@@ -0,0 +1,12 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+namespace leetcode::p0017 {
+
+// optimized: O(4^n * n) time (n = digits.size()), O(4^n * n) space — build
+// the combinations iteratively, one digit at a time.
+std::vector<std::string> solve(const std::string& digits);
+
+} // namespace leetcode::p0017
diff --git a/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/test.cpp b/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/test.cpp
new file mode 100644
index 0000000..0a99db1
--- /dev/null
+++ b/solutions/0001-0100/0017-letter-combinations-of-a-phone-number/test.cpp
@@ -0,0 +1,10 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include "solution.hpp"
+
+TEST_CASE("Problem 17", "[p0017]") {
+    CHECK(leetcode::p0017::solve("").empty());
+    CHECK(leetcode::p0017::solve("2") == std::vector<std::string>{"a", "b", "c"});
+    CHECK(leetcode::p0017::solve("23") ==
+          std::vector<std::string>{"ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"});
+}
diff --git a/swift/17.swift b/swift/17.swift
deleted file mode 100644
index 5f01622..0000000
--- a/swift/17.swift
+++ /dev/null
@@ -1,48 +0,0 @@
-class Solution {
-    let dict: [Character: [String]] = [
-        "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"]
-    ]
-
-    func letterCombinations(_ digits: String) -> [String] {
-        guard digits.count > 0 else {
-            return []
-        }
-
-        let letters = getLetters(digits)
-        return generateCombinations(letters)
-    }
-
-    private func getLetters(_ digits: String) -> [[String]] {
-        var letters: [[String]] = []
-        for digit in digits {
-            if let letter = dict[digit] {
-                letters.append(letter)
-            }
-        }
-        return letters
-    }
-
-    private func generateCombinations(_ letters: [[String]]) -> [String] {
-        var result: [String] = [""]
-        for letterGroup in letters {
-            var newResult: [String] = []
-            for combination in result {
-                for letter in letterGroup {
-                    newResult.append(combination + letter)
-                }
-            }
-            result = newResult
-        }
-        return result
-    }
-}
-
-let solution = Solution()
-print(solution.letterCombinations("23")) // ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]
\ No newline at end of file