adding new algos

Author: ivanpenaloza

src/my_project/interviews/amazon_high_frequency_23/round_2/longest_common_subsequence.py

@@ -0,0 +1,25 @@
+from typing import List, Union, Collection, Mapping, Optional
+
+class Solution:
+    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
+
+        # Make a grid of 0's with len(text2) + 1 columns 
+        # and len(text1) + 1 rows.
+        len_1 = len(text1)
+        len_2 = len(text2)
+        dp_grid = [[0]*(len_2+1) for _ in range(len_1+1)]
+
+
+        # Iterate up each column, starting from the last one. 
+        for j in reversed(range(len_2)):
+            for i in reversed(range(len_1)):
+                if text1[i] == text2[j]:
+                    dp_grid[i][j] = 1 + dp_grid[i+1][j+1]
+                else: 
+                    dp_grid[i][j] = max(dp_grid[i+1][j], dp_grid[i][j+1])
+
+
+        # The original problem's answer is in dp_grid[0][0]. Return it.  
+        return dp_grid[0][0]      
+    
+

src/my_project/interviews/amazon_high_frequency_23/round_2/number_of_islands.py

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+from typing import List, Union, Collection, Mapping, Optional
+from collections import deque
+
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        """BFS approach - explores island level by level"""
+
+        if not grid:
+            return 0
+        
+        rows, cols = len(grid), len(grid[0])
+        islands = 0
+
+        def bfs(r: int, c: int):
+            queue = deque([(r,c)])
+            grid[r][c] = '0'
+
+            while queue: 
+                row, col = queue.popleft()
+
+                for dr, dc in [(1,0), (-1,0), (0,1), (0,-1)]:
+                    nr, nc = row + dr, col + dc
+                    if (0 <= nr < rows and 0 <= nc < cols and grid[nr][nc] == '1'):
+                        grid[nr][nc] = '0'
+                        queue.append((nr,nc))
+
+        for r in range(rows):
+            for c in range(cols):
+                if grid[r][c] == '1':
+                    islands += 1
+                    bfs(r,c)
+
+        return islands
+    
+
+    def numIslands_DFS(grid: List[List[str]]) -> int:
+        """DFS approach - explores island depth-first"""
+
+        if not grid: 
+            return 0
+        
+        rows, cols = len(grid), len(grid[0])
+        islands = 0
+
+        def dfs(r: int, c: int):
+            if (r < 0 or r >= rows or c < 0 or c >= cols or grid[r][c] == '0'):
+                return 
+            
+            grid[r][c] = '0' 
+
+            dfs(r-1,c)
+            dfs(r+1,c)
+            dfs(r,c-1)
+            dfs(r,c+1)
+
+        for r in range(rows):
+            for c in range(cols):
+                if grid[r][c] == '1':
+                    islands += 1
+                    dfs(r,c)
+
+        return islands
+