Create Letter_Combinations_of_a_Phone_Number.cpp

backtracking_problems/Letter_Combinations_of_a_Phone_Number.cpp

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+class Solution {
+private:
+    void sol(string digits, string output, int index, vector<string>& ans, string map[]){
+
+        // base case
+        if (index > digits.length()) return;
+
+        if (index == digits.length()) {
+            ans.push_back(output);
+            return;
+        }
+
+        // If we dont subtract 0, then output will be given as a char since digits is a string
+        // But we need number in int --> so subtract 0
+        int number = digits[index] - '0';
+        string value = map[number];
+
+        for (int i = 0; i < value.length(); i++){
+            output.push_back(value[i]);
+            sol(digits, output, index + 1, ans, map);
+
+            // backtracking the changes made
+            output.pop_back();
+        }
+
+    }
+
+public:
+    vector<string> letterCombinations(string digits) {
+
+        vector <string> ans;
+        string output;
+        int index = 0;
+
+        // In case of empty string --> output will also be an empty arr
+        if (digits.length() == 0) return ans;
+
+        // Mapping index with corresponding strings
+        string map[10] = {" ", " ", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
+
+        sol(digits, output, index, ans, map);
+
+        return ans;
+    }
+
+};