Issue #95 is completed with a DFS algorithm

Author: Hamid Gasmi

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

@@ -1,18 +1,51 @@
-#Uses python3
-
 import sys
 
+class Graph:
+    def __init__(self, n, edges):
+        self.adj = [[] for _ in range(n)]
+        self.buildAdjacencyList(edges)
+    
+    # Time Complexity: O(|E|)
+    # Space Complexity: O(1)
+    def buildAdjacencyList(self, edges):
+        self.reset()
+
+        for (a, b) in edges:
+            self.adj[a - 1].append(b - 1)
+
+    def reset(self):
+        self.visited = [False] * len(self.adj)
+        self.removed = [False] * len(self.adj)
+
+    def explore(self, v):
+        self.visited[v] = True
+        for a in self.adj[v]:
+            if not self.removed[a]:
+                if self.visited[a]:
+                    return 1
+                if self.explore(a) == 1:
+                    return 1
+        
+        self.removed[v] = True
+        return 0
+
+    def DFS(self):
+        self.reset()
+        for v in range(len(self.adj)):
+            if (not self.removed[v]) and self.explore(v) == 1:
+                return 1
+        
+        return 0
+
+def acyclic(n, edges):
 
-def acyclic(adj):
-    return 0
+    aGraph = Graph(n, edges)
+    return aGraph.DFS()
 
 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]))
-    adj = [[] for _ in range(n)]
-    for (a, b) in edges:
-        adj[a - 1].append(b - 1)
-    print(acyclic(adj))
+    print(acyclic(n, edges))

3-graph-algorithms/1_graph_decomposition/acyclicity_tests/01

@@ -0,0 +1 @@
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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/01e

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/01r

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/02

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/02e

@@ -0,0 +1 @@
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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/02r

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/03

@@ -0,0 +1,4 @@
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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/03e

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/03r

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/04

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/04e

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/04r

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/05

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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/05e

@@ -0,0 +1 @@
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3-graph-algorithms/1_graph_decomposition/acyclicity_tests/05r

@@ -0,0 +1 @@
+0