From 4347ebe961a2300782f880a5d63b6fce147dda28 Mon Sep 17 00:00:00 2001
From: Haidong Ji
Date: Mon, 13 Jul 2020 22:02:36 -0500
Subject: Topological ordering done!

---
 sources/topsort.py | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 sources/topsort.py

diff --git a/sources/topsort.py b/sources/topsort.py
new file mode 100644
index 0000000..37f4ba0
--- /dev/null
+++ b/sources/topsort.py
@@ -0,0 +1,43 @@
+# Uses python3
+
+import sys
+
+
+def explore(v, adj, visited, postV, clock):
+    visited[v] = True
+    for w in adj[v]:
+        if visited[w] == False:
+            explore(w, adj, visited, postV, clock)
+    postV[v] = clock[0]
+    clock[0] = clock[0] + 1
+
+
+def dfs(adj, visited, postV, clock):
+    for v in range(len(adj)):
+        if visited[v] == False:
+            explore(v, adj, visited, postV, clock)
+
+
+def toposort(adj):
+    visited = [False] * len(adj)
+    order = []
+    postV = [0] * len(adj)
+    clock = [0]
+
+    dfs(adj, visited, postV, clock)
+    order = sorted(range(len(postV)), key=lambda k: postV[k], reverse=True)
+    return order
+
+
+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)
+    order = toposort(adj)
+    for x in order:
+        print(x + 1, end=' ')
-- 
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