From d1279cbec51ce102edcadcd9a1827b4762d2b01b Mon Sep 17 00:00:00 2001
From: Bruno Freitas Tissei <bft15@inf.ufpr.br>
Date: Mon, 12 Feb 2018 16:34:13 -0200
Subject: [PATCH] Add topological_sort
Signed-off-by: Bruno Freitas Tissei <bft15@inf.ufpr.br>
---
graph/topological_sort.cpp | 48 ++++++++++++++++++++++++++++++++++++++
1 file changed, 48 insertions(+)
create mode 100644 graph/topological_sort.cpp
diff --git a/graph/topological_sort.cpp b/graph/topological_sort.cpp
new file mode 100644
index 0000000..b06a4db
--- /dev/null
+++ b/graph/topological_sort.cpp
@@ -0,0 +1,48 @@
+/**
+ * Topological Sort
+ *
+ * Complexity (Time): O(n + m)
+ * Complexity (Space): O(n + m)
+ */
+
+stack<int> S;
+vector<int> graph[MAX];
+
+int cont[MAX];
+
+// Fill stack and check for cycles
+bool dfs(int x) {
+ cont[x] = 1;
+
+ for (auto i : graph[x]) {
+ if (cont[i] == 1)
+ return true;
+ if (!cont[i] && dfs(i))
+ return true;
+ }
+
+ cont[x] = 2;
+ S.push(x);
+
+ return false;
+}
+
+// Return topological sort of graph with n vertices
+bool topological_sort(int n, vector<int> &tsort) {
+ memset(cont, 0, sizeof cont);
+
+ bool cycle = false;
+ for (int i = 0; i < n; ++i)
+ if (!cont[i])
+ cycle |= dfs(i);
+
+ if (cycle)
+ return true;
+
+ while (!S.empty()) {
+ tsort.push_back(S.top());
+ S.pop();
+ }
+
+ return false;
+}
--
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