init

1N.py

@@ -0,0 +1,74 @@
+import sys
+
+data = sys.stdin.read().split()
+if not data:
+    exit()
+n = int(data[0])
+m = int(data[1])
+adj_all = [[] for _ in range(n + 1)]
+adj2 = [[] for _ in range(n + 1)]
+rev_adj2 = [[] for _ in range(n + 1)]
+edges2 = []
+idx = 2
+for _ in range(m):
+    u = int(data[idx])
+    v = int(data[idx+1])
+    t = int(data[idx+2])
+    idx += 3
+    adj_all[u].append(v)
+    if t == 2:
+        adj2[u].append(v)
+        rev_adj2[v].append(u)
+        edges2.append((u, v))
+reachable = [False] * (n + 1)
+reachable[1] = True
+q = [1]
+head = 0
+while head < len(q):
+    u = q[head]
+    head += 1
+    for v in adj_all[u]:
+        if not reachable[v]:
+            reachable[v] = True
+            q.append(v)
+visited = [False] * (n + 1)
+order = []
+edge_idx = [0] * (n + 1)
+stack = []
+for i in range(1, n + 1):
+    if not visited[i]:
+        visited[i] = True
+        stack.append(i)
+        while stack:
+            u = stack[-1]
+            if edge_idx[u] < len(adj2[u]):
+                v = adj2[u][edge_idx[u]]
+                edge_idx[u] += 1
+                if not visited[v]:
+                    visited[v] = True
+                    stack.append(v)
+            else:
+                order.append(u)
+                stack.pop()
+scc_id = [0] * (n + 1)
+current_scc = 0
+for i in range(n - 1, -1, -1):
+    start_node = order[i]
+    if scc_id[start_node] == 0:
+        current_scc += 1
+        q_scc = [start_node]
+        scc_id[start_node] = current_scc
+        head_scc = 0
+        while head_scc < len(q_scc):
+            u = q_scc[head_scc]
+            head_scc += 1
+            for v in rev_adj2[u]:
+                if scc_id[v] == 0:
+                    scc_id[v] = current_scc
+                    q_scc.append(v)
+ans = "No"
+for u, v in edges2:
+    if reachable[u] and scc_id[u] != scc_id[v]:
+        ans = "Yes"
+        break
+print(ans)