day 19-q3 added in python SnowScriptWinterOfCode#418

Day-19/q3-Letter Combinations of a Phone Number/Tech-neophyte--p.md

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+## Approach:
+<br /> 1. Initialize a Mapping: Create a dictionary that maps each digit from 2 to 9 to their corresponding letters on a telephone's buttons.
+<br /> 2. Base Case: If the input string digits is empty, return an empty list.
+<br /> 3. Iteratively make Combinations: Start with an empty combination in a list and iteratively build the combinations by processing each digit in the input string.
+For each existing combination, append each corresponding letter for the current digit, building new combinations.
+<br /> 4. Result: Return the generated combinations as the final result.
+## Python code:
+```
+class Solution:
+    def letterCombinations(self, digits: str) -> List[str]:
+        if not digits:
+            return []
+
+        phone_map = {
+            '2': 'abc',
+            '3': 'def',
+            '4': 'ghi',
+            '5': 'jkl',
+            '6': 'mno',
+            '7': 'pqrs',
+            '8': 'tuv',
+            '9': 'wxyz'
+        }
+        combinations=[""]
+        for i in digits:
+            new_comb=[]
+            for j  in combinations:
+                for l in phone_map[i]:
+                    new_comb.append(j+l)
+            combinations=new_comb
+        return combinations
+        
+
+```