s0017

include/s0017_letter_combinations_of_a_phone_number.hpp

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+#ifndef S0017_LETTER_COMBINATIONS_OF_A_PHONE_NUMBER
+#define S0017_LETTER_COMBINATIONS_OF_A_PHONE_NUMBER
+
+#include <vector>
+#include <string>
+#include <unordered_map>
+
+using namespace std;
+
+class Solution {
+ public:
+  vector<string> letterCombinations(string digits);
+};
+
+#endif

src/s0017_letter_combinations_of_a_phone_number.cpp

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+#include "s0017_letter_combinations_of_a_phone_number.hpp"
+
+vector<string> Solution::letterCombinations(string digits) {
+  unordered_map<string, vector<string>> map;
+  map["2"] = vector<string>{"a", "b", "c"};
+  map["3"] = vector<string>{"d", "e", "f"};
+  map["4"] = vector<string>{"g", "h", "i"};
+  map["5"] = vector<string>{"j", "k", "l"};
+  map["6"] = vector<string>{"m", "n", "o"};
+  map["7"] = vector<string>{"p", "q", "r", "s"};
+  map["8"] = vector<string>{"t", "u", "v"};
+  map["9"] = vector<string>{"w", "x", "y", "z"};
+  if (digits.length() == 0) {
+    return vector<string>{};
+  } else {
+    string last = digits.substr(digits.length() - 1, 1);
+    digits.pop_back();
+    vector<string> combinations = letterCombinations(digits);
+    if (combinations.size() == 0) {
+      combinations = {""};
+    }
+    vector<string> result = {};
+    for (int i{0}; i < map.at(last).size(); i++) {
+      vector<string> temp = combinations;
+      for (int j{0}; j < temp.size(); j++) {
+        temp[j] += map.at(last)[i];
+      }
+      result.insert(result.end(), temp.begin(), temp.end());
+    }
+    return result;
+  }
+}

tests/s0017_letter_combinations_of_a_phone_number.cpp

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+#include "s0017_letter_combinations_of_a_phone_number.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(Problem17, Case1) {
+  string i{"23"};
+  vector<string> o{"ad", "bd", "cd", "ae", "be", "ce", "af", "bf", "cf"};
+  Solution solution;
+  EXPECT_EQ(solution.letterCombinations(i), o);
+}
+
+TEST(Problem17, Case2) {
+  string i{""};
+  vector<string> o{};
+  Solution solution;
+  EXPECT_EQ(solution.letterCombinations(i), o);
+}
+
+TEST(Problem17, Case3) {
+  string i{"2"};
+  vector<string> o{"a", "b", "c"};
+  Solution solution;
+  EXPECT_EQ(solution.letterCombinations(i), o);
+}