Issue #87 is completed with Bi-Directional BFS

Author: Hamid Gasmi

3-graph-algorithms/1_graph_decomposition/reachability_parralel_bfs.py

@@ -0,0 +1,84 @@
+import sys
+from queue import Queue
+import threading
+
+class MazeGraph:
+    
+    result = 0
+    s = set()
+    lock = threading.Lock()
+
+    def __init__(self, n, adj):
+        self.adj = adj
+        self.visited = [False] * n
+        self.enqueued = [False] * n
+        self.q = Queue(n)
+
+    def visit(self, v):
+        self.visited[v] = True
+
+        if v in MazeGraph.s:
+            MazeGraph.lock.acquire()
+            MazeGraph.result = 1
+            endThread = True
+            MazeGraph.lock.release()
+        else:
+            MazeGraph.lock.acquire()
+            MazeGraph.s.add(v)
+            MazeGraph.lock.release()
+            endThread = MazeGraph.result == 1
+
+        return endThread
+
+    def isVisited(self, v, visited):
+        return visited[v]
+
+    def enqueue(self, v):
+        if not self.enqueued[v]:
+            self.q.put(v)
+            self.enqueued[v] = True
+
+    # Time Complexity: O(|V| + |E|)
+    # Space Complexity: O(|V|):
+    def explore(self, u):
+        self.enqueue(u)
+        while not self.q.empty():
+            u = self.q.get()
+            if self.visit(u):
+                return 1
+
+            for i in range(len(self.adj[u])):
+                self.enqueue(self.adj[u][i])
+
+        return 0
+
+def reach(n, edges, u, v):
+    adj = [[] for _ in range(n)]
+    for (a, b) in edges:
+        adj[a - 1].append(b - 1)
+        adj[b - 1].append(a - 1)
+
+    aMaze1 = MazeGraph(n, adj)
+    aMaze2 = MazeGraph(n, adj)
+
+    t1 = threading.Thread(target=aMaze1.explore, args=(u, ))
+    t2 = threading.Thread(target=aMaze2.explore, args=(v, ))
+
+    t1.start()
+    t2.start()
+
+    t1.join()
+    t2.join()
+
+    return MazeGraph.result
+
+if __name__ == '__main__':
+    input = sys.stdin.read()
+    data = list(map(int, input.split()))
+    n, m = data[0:2]
+    data = data[2:]
+    edges = list(zip(data[0:(2 * m):2], data[1:(2 * m):2]))
+    x, y = data[2 * m:]
+    x, y = x - 1, y - 1
+
+    print(reach(n, edges, x, y))