Graph1:All Done

Find the Town Judge.py

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+'''
+Solution : In-Degrees array
+    For a relationship a-->Trusts-->b
+        - +1 for b
+        - -1 for a 
+    At the end, if in_degrees of a person == n-1, we found the judge
+Time Complexity: O(N) 
+Space Complexity: O(N) 
+'''
+class Solution:
+    def findJudge(self, n: int, trust: List[List[int]]) -> int:
+        in_degrees = [0]*n 
+
+        for relationship in trust:
+            a = relationship[0]
+            b = relationship[1]
+
+            # a trusts b (people are 1->n indexed)
+            in_degrees[b-1]+=1 # increse count of people trusting b
+            in_degrees[a-1]-=1 # decrease count of 'a' as it's trusting someone
+
+        for person_label in range(len(in_degrees)):
+            if in_degrees[person_label]==n-1: # n-1 people trusting and this person not trusting anyone else
+                return person_label+1 # Found judge. 
+
+        return -1 # No Judge
+

The Maze.py

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+'''
+Solution: BFS 
+Time complexity: O(m*n)
+Space Complexity: O(m*n)
+'''
+class Solution:
+    def hasPath(self, maze: List[List[int]], start: List[int], destination: List[int]) -> bool:
+        rows = len(maze)
+        cols = len(maze[0])
+
+        bfs_queue = deque() 
+
+        bfs_queue.append(start)
+        maze[start[0]][start[1]] = 2 # mark visited
+
+        while bfs_queue:
+            parent_row, parent_col = bfs_queue.popleft()
+
+            # Try rolling ball to right:
+            row = parent_row
+            col = parent_col
+
+            while col<cols and maze[row][col]!=1:
+                col+=1
+            col=col-1 # where ball stopped
+
+            if [row,col]==destination: # ball stoped at target
+                return True
+
+            if maze[row][col]!=2:
+                bfs_queue.append([row,col])
+                maze[row][col]=2
+
+            # Try rolling ball down:
+            row = parent_row
+            col = parent_col
+
+            while row<rows and maze[row][col]!=1:
+                row+=1
+            row=row-1 # where ball stopped
+
+            if [row,col]==destination: # ball stoped at target
+                return True
+
+            if maze[row][col]!=2:
+                bfs_queue.append([row,col])
+                maze[row][col]=2
+
+            # Try rolling ball to left:
+            row = parent_row
+            col = parent_col
+
+            while col>=0 and maze[row][col]!=1:
+                col-=1
+            col=col+1 # where ball stopped
+
+            if [row,col]==destination: # ball stoped at target
+                return True
+
+            if maze[row][col]!=2:
+                bfs_queue.append([row,col])
+                maze[row][col]=2
+
+            # Try rolling ball upwards:
+            row = parent_row
+            col = parent_col
+
+            while row>=0 and maze[row][col]!=1:
+                row-=1
+            row=row+1 # where ball stopped
+
+            if [row,col]==destination: # ball stoped at target
+                return True
+
+            if maze[row][col]!=2:
+                bfs_queue.append([row,col])
+                maze[row][col]=2
+
+        return False