adding algo

src/my_project/interviews/amazon_high_frequency_23/common_algos/two_sum_round_2.py

@@ -0,0 +1,21 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+
+        answer = dict()
+
+        for k, v in enumerate(nums):
+
+            if v in answer: 
+                return [answer[v], k]
+            else: 
+                answer[target - v] = k 
+
+        return []
+
+
+
+
+

src/my_project/interviews/amazon_high_frequency_23/common_algos/valid_palindrome_round_2.py

@@ -0,0 +1,22 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+import re
+
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+
+        # To lowercase
+        s = s.lower()
+
+        # Remove non-alphanumeric characters
+        s = re.sub(pattern=r'[^a-zA-Z0-9]', repl='', string=s)
+
+        # Determine if s is palindrome or not
+        len_s = len(s)
+
+        for i in range(len_s//2):
+
+            if s[i] != s[len_s - 1 - i]:
+                return False 
+
+        return True 

src/my_project/interviews/top_150_questions_round_22/ex_92_word_ladder.py

@@ -0,0 +1,63 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+from collections import deque, defaultdict
+
+class Solution:
+    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:
+        """
+        Find the shortest transformation sequence from beginWord to endWord.
+        Uses BFS to find the shortest path.
+
+        Time Complexity: O(M^2 * N) where M is word length, N is wordList size
+        Space Complexity: O(M^2 * N) for the pattern dictionary
+        """
+        # If beginWord equals endWord, the sequence is just the word itself
+        if beginWord == endWord:
+            return 1
+
+        # If endWord is not in wordList, no valid transformation exists
+        if endWord not in wordList:
+            return 0
+
+        # Convert wordList to set for O(1) lookup
+        word_set = set(wordList)
+
+        # Build a pattern dictionary to find all words that differ by one letter
+        # e.g., "hot" -> {"*ot": ["hot"], "h*t": ["hot"], "ho*": ["hot"]}
+        pattern_dict = defaultdict(list)
+        word_len = len(beginWord)
+
+        # Add beginWord to the set if not present
+        if beginWord not in word_set:
+            word_set.add(beginWord)
+
+        # Create patterns for all words
+        for word in word_set:
+            for i in range(word_len):
+                pattern = word[:i] + '*' + word[i+1:]
+                pattern_dict[pattern].append(word)
+
+        # BFS to find shortest path
+        queue = deque([(beginWord, 1)])  # (current_word, level)
+        visited = {beginWord}
+
+        while queue:
+            current_word, level = queue.popleft()
+
+            # Try all possible transformations by replacing each character
+            for i in range(word_len):
+                pattern = current_word[:i] + '*' + current_word[i+1:]
+
+                # Get all words matching this pattern
+                for next_word in pattern_dict[pattern]:
+                    if next_word == endWord:
+                        return level + 1
+
+                    if next_word not in visited:
+                        visited.add(next_word)
+                        queue.append((next_word, level + 1))
+
+                # Clear the pattern to avoid revisiting in future iterations
+                pattern_dict[pattern] = []
+
+        return 0

src/my_project/interviews_typescript/top_150_questions_round_1/ex_92_word_ladder.ts

@@ -0,0 +1,75 @@
+function ladderLength(beginWord: string, endWord: string, wordList: string[]): number {
+    /**
+     * Find the shortest transformation sequence from beginWord to endWord.
+     * Uses BFS to find the shortest path.
+     * 
+     * Time Complexity: O(M^2 * N) where M is word length, N is wordList size
+     * Space Complexity: O(M^2 * N) for the pattern dictionary
+     */
+
+    // If beginWord equals endWord, the sequence is just the word itself
+    if (beginWord === endWord) {
+        return 1;
+    }
+
+    // If endWord is not in wordList, no valid transformation exists
+    if (!wordList.includes(endWord)) {
+        return 0;
+    }
+
+    // Convert wordList to set for O(1) lookup
+    const wordSet = new Set<string>(wordList);
+
+    // Add beginWord to the set if not present
+    if (!wordSet.has(beginWord)) {
+        wordSet.add(beginWord);
+    }
+
+    // Build a pattern dictionary to find all words that differ by one letter
+    // e.g., "hot" -> {"*ot": ["hot"], "h*t": ["hot"], "ho*": ["hot"]}
+    const patternDict = new Map<string, string[]>();
+    const wordLen = beginWord.length;
+
+    // Create patterns for all words
+    for (const word of wordSet) {
+        for (let i = 0; i < wordLen; i++) {
+            const pattern = word.slice(0, i) + '*' + word.slice(i + 1);
+            if (!patternDict.has(pattern)) {
+                patternDict.set(pattern, []);
+            }
+            patternDict.get(pattern)!.push(word);
+        }
+    }
+
+    // BFS to find shortest path
+    const queue: [string, number][] = [[beginWord, 1]]; // [current_word, level]
+    const visited = new Set<string>([beginWord]);
+
+    while (queue.length > 0) {
+        const [currentWord, level] = queue.shift()!;
+
+        // Try all possible transformations by replacing each character
+        for (let i = 0; i < wordLen; i++) {
+            const pattern = currentWord.slice(0, i) + '*' + currentWord.slice(i + 1);
+
+            // Get all words matching this pattern
+            const neighbors = patternDict.get(pattern) || [];
+            for (const nextWord of neighbors) {
+                if (nextWord === endWord) {
+                    return level + 1;
+                }
+
+                if (!visited.has(nextWord)) {
+                    visited.add(nextWord);
+                    queue.push([nextWord, level + 1]);
+                }
+            }
+
+            // Clear the pattern to avoid revisiting in future iterations
+            patternDict.set(pattern, []);
+        }
+    }
+
+    return 0;
+}
+

tests/test_150_questions_round_22/test_92_word_ladder_round_22.py

@@ -0,0 +1,79 @@
+import pytest
+from src.my_project.interviews.top_150_questions_round_22.ex_92_word_ladder import Solution
+
+
+class TestWordLadder:
+    def setup_method(self):
+        self.solution = Solution()
+
+    def test_example_1(self):
+        """Test Example 1: Standard transformation sequence"""
+        beginWord = "hit"
+        endWord = "cog"
+        wordList = ["hot", "dot", "dog", "lot", "log", "cog"]
+
+        result = self.solution.ladderLength(beginWord, endWord, wordList)
+        assert result == 5, "Should return 5 for the sequence: hit -> hot -> dot -> dog -> cog"
+
+    def test_example_2(self):
+        """Test Example 2: endWord not in wordList"""
+        beginWord = "hit"
+        endWord = "cog"
+        wordList = ["hot", "dot", "dog", "lot", "log"]
+
+        result = self.solution.ladderLength(beginWord, endWord, wordList)
+        assert result == 0, "Should return 0 when endWord is not in wordList"
+
+    def test_single_transformation(self):
+        """Test single transformation"""
+        beginWord = "hot"
+        endWord = "dot"
+        wordList = ["hot", "dot"]
+
+        result = self.solution.ladderLength(beginWord, endWord, wordList)
+        assert result == 2, "Should return 2 for direct transformation"
+
+    def test_no_transformation_needed(self):
+        """Test when begin and end are same"""
+        beginWord = "hot"
+        endWord = "hot"
+        wordList = ["hot"]
+
+        result = self.solution.ladderLength(beginWord, endWord, wordList)
+        assert result == 1, "Should return 1 when beginWord equals endWord"
+
+    def test_no_path_exists(self):
+        """Test when no valid path exists"""
+        beginWord = "hit"
+        endWord = "cog"
+        wordList = ["hot", "dot", "tog"]
+
+        result = self.solution.ladderLength(beginWord, endWord, wordList)
+        assert result == 0, "Should return 0 when no valid transformation sequence exists"
+
+    def test_longer_words(self):
+        """Test with longer words"""
+        beginWord = "teach"
+        endWord = "place"
+        wordList = ["teach", "peach", "peace", "place", "reach"]
+
+        result = self.solution.ladderLength(beginWord, endWord, wordList)
+        assert result == 4, "Should return 4 for: teach -> peach -> peace -> place"
+
+    def test_multiple_paths(self):
+        """Test when multiple paths exist"""
+        beginWord = "red"
+        endWord = "tax"
+        wordList = ["ted", "tex", "red", "tax", "tad", "rex"]
+
+        result = self.solution.ladderLength(beginWord, endWord, wordList)
+        assert result == 4, "Should return 4 for shortest path: red -> ted -> tex -> tax"
+
+    def test_empty_word_list(self):
+        """Test with empty wordList"""
+        beginWord = "hit"
+        endWord = "cog"
+        wordList = []
+
+        result = self.solution.ladderLength(beginWord, endWord, wordList)
+        assert result == 0, "Should return 0 when wordList is empty"