2

Author: kedebug

LetterCombinationsofaPhoneNumber/LetterCombinationsofaPhoneNumber.cpp

@@ -0,0 +1,27 @@
+
+const string Solution::keypad[8] = {"abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
+
+class Solution {
+public:
+    static const string keypad[8];
+    vector<string> letterCombinations(string digits) {
+        // Start typing your C/C++ solution below
+        // DO NOT write int main() function
+        
+        vector<string> all_letters;
+        string letter;
+        letterCombinationsHelper(digits, 0, letter, all_letters);
+    }
+    void letterCombinationsHelper(string& digits, int step, string& letter, vector<string>& all_letters) {
+        if (step == digits.size()) {
+            all_letters.push_back(letter);
+            return;
+        }
+        int x = digits[step] - '2';
+        for (int i = 0; i < keypad[x].size(); i++) {
+            letter += keypad[x][i];
+            letterCombinationsHelper(digits, step + 1, letter, all_letters);
+            letter.erase(letter.size() - 1, 1);
+        }
+    }
+};