Create Letter Combinations of a Phone Number.cpp

Cpp/Letter Combinations of a Phone Number.cpp

@@ -0,0 +1,37 @@
+/*
+Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.
+
+A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.
+*/
+
+class Solution {
+public:
+    string str="";
+    void find(int i, string s, vector<string>&v, map<int,vector<char>>&m){
+        if(i==s.length()){
+            v.push_back(str);
+            return;
+        }
+        for(int j=0; j<m[s[i]-'0'].size(); j++){
+            str.push_back(m[s[i]-'0'][j]);
+            find(i+1,s,v,m);
+            str.pop_back();
+        }
+    }
+    vector<string> letterCombinations(string digits) {
+        map<int,vector<char>>m;
+        int j=1;
+        for(int i=0; i<26; i++){
+            if(i%3==0 && i<18){
+                j++;
+            }
+            if(i==19) j++;
+            if(i==22) j++;
+            m[j].push_back('a'+i);
+        }
+        vector<string>v;
+        if(digits=="") return v;
+        find(0,digits,v,m);
+        return v;
+    }
+};