april 8

Author: YuriSpiridonov

Challenges/2021/April-LeetCoding-Challenge.md

@@ -21,5 +21,10 @@ None
 |1551.|[Minimum Operations to Make Array Equal](https://leetcode.com/problems/minimum-operations-to-make-array-equal/)|[Python](/Medium/1551.MinimumOperationstoMakeArrayEqual.py)|Medium|
 |1704.|[Determine if String Halves Are Alike](https://leetcode.com/problems/determine-if-string-halves-are-alike/)|[Python](/Easy/1704.DetermineifStringHalvesAreAlike.py)|Easy|
 
+## Week 2
+|№|Title|Solution|Difficulty|
+| ----: | --- | --- | --- |
+|17.|[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)|[Python](/Medium/17.LetterCombinationsofaPhoneNumber.py)|Medium|
+
 ## License
 The code is open-source and licensed under the [MIT License](/LICENSE).

Medium/17.LetterCombinationsofaPhoneNumber.py

@@ -0,0 +1,46 @@
+'''
+    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 digit to letters (just like on the 
+    telephone buttons) is given below. Note that 1 does not 
+    map to any letters.
+
+    Example:
+    Input: digits = "23"
+    Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
+
+    Example:
+    Input: digits = ""
+    Output: []
+
+    Example:
+    Input: digits = "2"
+    Output: ["a","b","c"]
+
+    Constraints:
+        - 0 <= digits.length <= 4
+        - digits[i] is a digit in the range ['2', '9'].
+'''
+#Difficulty: Medium
+#25 / 25 test cases passed.
+#Runtime: 28 ms
+#Memory Usage: 14.2 MB
+
+#Runtime: 28 ms, faster than 81.79% of Python3 online submissions for Letter Combinations of a Phone Number.
+#Memory Usage: 14.2 MB, less than 86.13% of Python3 online submissions for Letter Combinations of a Phone Number.
+
+class Solution:
+    def letterCombinations(self, digits: str) -> List[str]:
+        length = len(digits)
+        letters = {'2': 'abc', '3': 'def', '4': 'ghi', '5': 'jkl', '6': 'mno', '7': 'pqrs', '8': 'tuv', '9': 'wxyz'}
+        return self.dfs(digits, letters, length, [], '', 0)
+    
+    def dfs(self, digits, letters, length, result, combination, current):
+        if current == length:
+            result.append(combination)
+            return
+        for char in letters[digits[current]]:
+            self.dfs(digits, letters, length, result, combination+char, current+1)
+        return result

README.md

@@ -1,6 +1,6 @@
 # Python solutions of LeetCode problems.
 ![Language](https://img.shields.io/badge/language-Python-blue.svg) 
-![Problems Solved](https://img.shields.io/badge/problems%20solved-531%2F1637-orange) 
+![Problems Solved](https://img.shields.io/badge/problems%20solved-532%2F1637-orange) 
 [![License](https://img.shields.io/badge/license-MIT-green.svg)](./LICENSE) 
 ![Update](https://img.shields.io/badge/update-Daily-brightgreen.svg) 
 <br><br>
@@ -22,7 +22,7 @@ In this repository provided my Python solutions of LeetCode problems.
 - [January LeetCoding Challenge](/Challenges/2021/January-LeetCoding-Challenge.md) - 27/31
 - [February LeetCoding Challenge](/Challenges/2021/February-LeetCoding-Challenge.md) - 23/28
 - [March LeetCoding Challenge](/Challenges/2021/March-LeetCoding-Challenge.md) - 23/31
-- [April LeetCoding Challenge](/Challenges/2021/April-LeetCoding-Challenge.md) - 5/30
+- [April LeetCoding Challenge](/Challenges/2021/April-LeetCoding-Challenge.md) - 6/30
 <br><br>
 ## Solutions
 *P.S. If you like this, please leave me a star.* ★
@@ -42,6 +42,7 @@ In this repository provided my Python solutions of LeetCode problems.
 |14.|[Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/)|[Python](https://github.com/YuriSpiridonov/LeetCode/blob/master/Easy/14.LongestCommonPrefix.py)|Easy||
 |15.|[3Sum](https://leetcode.com/problems/3sum/)|[Python](/Medium/15.3Sum(bruteforce).py)|Medium|Brute Force|
 |16.|[3Sum Closest](https://leetcode.com/problems/3sum-closest/)|[Python](/Medium/16.3SumClosest(bruteforce).py)|Medium|Brute Force|
+|17.|[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)|[Python](/Medium/17.LetterCombinationsofaPhoneNumber.py)|Medium|`DFS`, `Recursion`|
 |19.|[Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)|[Python](/Medium/19.RemoveNthNodeFromEndofList.py)|Medium|`Stack`|
 |20.|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)|[Python](/Easy/20.ValidParentheses(BruteForce).py)|Easy|Brute Force|
 |20.|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)|[Python](/Easy/20.ValidParentheses(Stack).py)|Easy|`Stack`|