#170 is started

Author: Hamid Gasmi

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag.py

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+import sys
+from collections import namedtuple
+
+Edge = namedtuple('Edge', ['v', 'w'])
+
+class Directed_Acyclic_Graph:
+    def __init__(self, source, sink, edges):
+        
+        self.v_no_label_gap = source #v_no are 0-based index but input labels could start at any position
+        self.vertices_count = sink - source + 1
+        self.is_valid_dag = True
+        
+        self.build_adjacency_list(edges)
+        self.check_dag_dfs()
+
+        #print(self.adjacency_list)
+        #print("self.is_valid_source: ", self.is_valid_source)
+        #print("self.is_valid_sink: ", self.is_valid_sink)
+        #print("self.is_valid_dag: ", self.is_valid_dag)
+        
+    def build_adjacency_list(self, edges):
+        
+        self.adjacency_list = [[] for _ in range(self.vertices_count)]
+
+        self.is_valid_source = True
+        self.is_valid_sink = False
+        for edge in edges:
+            u = int(edge.split("->")[0]) - self.v_no_label_gap
+            v = int(edge.split("->")[1].split(":")[0]) - self.v_no_label_gap
+            w = int(edge.split("->")[1].split(":")[1])
+
+            self.adjacency_list[u].append(Edge(v, w))
+            
+            self.is_valid_source &= (v != 0)
+            self.is_valid_sink |= (v == self.vertices_count - 1)
+            
+            #print(self.adjacency_list)
+        
+        self.is_valid_source &= (len(self.adjacency_list[0]) > 0)
+        self.is_valid_sink &= len(self.adjacency_list[self.vertices_count - 1]) == 0
+        
+    def explore_path(self, u, visited, cycle):
+        
+        visited[u] = True
+        cycle[u] = True
+        for edge in self.adjacency_list[u]:
+
+            if cycle[edge.v]:
+                return True
+            
+            if visited[edge.v]:
+                continue
+            
+            if self.explore_path(edge.v, visited, cycle):
+                return True
+
+        cycle[u] = False
+
+        return False
+
+    def check_dag_dfs(self):
+
+        visited = [False for _ in range(self.vertices_count)] 
+        cycle  = [False for _ in range(self.vertices_count)] 
+
+        self.is_valid_dag = True
+        for v in range(self.vertices_count):
+            if not visited[v]:
+                if self.explore_path(v, visited, cycle):
+                    self.is_valid_dag = False
+                    break
+    
+    def compute_longest_path(self, source, sink):
+        self.longest_path_len = 0
+        self.longest_path = []
+
+        if not self.is_valid_dag:
+            return
+        
+        # TODO: your code here
+        return ""
+
+    def longest_path_to_str(self):
+
+        return '->'.join(self.longest_path)
+
+if __name__ == "__main__":
+
+    source = int(sys.stdin.readline().strip())
+    sink = int(sys.stdin.readline().strip())
+    edges = [line.strip() for line in sys.stdin]
+
+    dag = Directed_Acyclic_Graph(source, sink, edges)
+    dag.compute_longest_path(source, sink)
+
+    print(dag.longest_path_len)
+    #print(dag.longest_path_to_str)

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag_tests/01

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+0
+4
+2->3:2
+1->4:1
+3->4:3
+4->3:3

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag_tests/02

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+0
+4
+0->1:7
+0->2:4
+2->3:2
+1->4:1
+3->4:3
+4->3:3

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag_tests/03

@@ -0,0 +1,7 @@
+0
+4
+0->1:7
+0->2:4
+2->3:2
+1->4:1
+3->4:3

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag_tests/04

@@ -0,0 +1,6 @@
+0
+3
+0->1:1
+0->3:10
+1->2:1
+2->3:1

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag_tests/05

@@ -0,0 +1,6 @@
+0
+3
+0->1:2
+0->2:1
+1->3:3
+2->3:3

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag_tests/06

@@ -0,0 +1,6 @@
+0
+3
+0->1:1
+0->2:5
+1->3:10
+2->3:1

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag_tests/07

@@ -0,0 +1,6 @@
+1
+4
+1->2:1
+1->3:5
+2->4:10
+3->4:1

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag_tests/08

@@ -0,0 +1,5 @@
+1
+10
+1->2:1
+2->3:3
+3->10:1

6-dynamic-programming-applications-in-machine-learning-and-genomics/1-sequence-alignment-1/longest_path_dag_tests/09

@@ -0,0 +1,3 @@
+0
+4
+0->4:7