init

1H.py

@@ -0,0 +1,41 @@
+n, m, s, t = map(int, input().split())
+
+graph = [[] for _ in range(n + 1)]
+in_degree = [0] * (n + 1)
+
+for _ in range(m):
+    u, v, weight = map(int, input().split())
+    graph[u].append((v, weight))
+    in_degree[v] += 1
+
+queue = []
+for i in range(1, n + 1):
+    if in_degree[i] == 0:
+        queue.append(i)
+
+order = []
+head = 0
+
+while head < len(queue):
+    current = queue[head]
+    head += 1
+    order.append(current)
+    
+    for neighbor, weight in graph[current]:
+        in_degree[neighbor] -= 1
+        if in_degree[neighbor] == 0:
+            queue.append(neighbor)
+
+dist = [10**18] * (n + 1)
+dist[s] = 0
+
+for node in order:
+    if dist[node] != 10**18:
+        for neighbor, weight in graph[node]:
+            if dist[node] + weight < dist[neighbor]:
+                dist[neighbor] = dist[node] + weight
+
+if dist[t] == 10**18:
+    print("Unreachable")
+else:
+    print(dist[t])