Letter Combinations of a Phone Number

Author: Shikha-code36

Backtracking/17-Letter-Combinations-of-a-Phone-Number.py

@@ -0,0 +1,41 @@
+'''Leetcode- https://leetcode.com/problems/letter-combinations-of-a-phone-number/ '''
+'''
+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.
+
+Example 1:
+
+Input: digits = "23"
+Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
+
+'''
+
+def letterCombinations(digits):
+    res = []
+    digitToChar = { "2": "abc",
+                    "3": "def",
+                    "4": "ghi",
+                    "5": "jkl",
+                    "6": "mno",
+                    "7": "qprs",
+                    "8": "tuv",
+                    "9": "wxyz"}
+    
+    def backtrack(i,cur):
+        if len(cur) == len(digits):
+            res.append(cur)
+            return
+
+        for j in digitToChar[digits[i]]:
+            backtrack(i+1,cur+j)
+
+    if digits:
+        backtrack(0,"")
+    
+    return res
+
+#T:O(n.4^n)
+#S:O(n)
+
+

README.md

@@ -18,5 +18,6 @@ Check the notes for the explaination - [Notes](https://stingy-shallot-4ea.notion
     - [x] [Combination Sum III](Backtracking/216-Combination-Sum-III.py)
     - [x] [Generate Parentheses](Backtracking/22-Generate-Parentheses.py)
     - [x] [Palindrome Partitioning](Backtracking/131-Palindrome-Partitioning.py)
+    - [x] [Letter Combinations of a Phone Number](Backtracking/17-Letter-Combinations-of-a-Phone-Number.py)