From d36c75251f4bcd1ee5ff6ac80103dc431a446557 Mon Sep 17 00:00:00 2001
From: Bruno Freitas Tissei <bft15@inf.ufpr.br>
Date: Wed, 16 May 2018 23:23:01 +0200
Subject: [PATCH] Add tarjan algorithm
Signed-off-by: Bruno Freitas Tissei <bft15@inf.ufpr.br>
---
graph/tarjan.cpp | 53 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 53 insertions(+)
create mode 100644 graph/tarjan.cpp
diff --git a/graph/tarjan.cpp b/graph/tarjan.cpp
new file mode 100644
index 0000000..f9e1952
--- /dev/null
+++ b/graph/tarjan.cpp
@@ -0,0 +1,53 @@
+/**
+ * Tarjan - Strongly Connected Components
+ *
+ * Complexity (Time): O(n + m)
+ * Complexity (Space): O(n + m)
+ */
+
+vector<int> graph[MAX];
+vector<int> scc[MAX];
+
+stack<int> S;
+int ncomp, ind;
+int cont[MAX], parent[MAX];
+int low[MAX], L[MAX];
+
+// Fills scc with strongly connected components of graph
+void dfs(int x) {
+ L[x] = ind;
+ low[x] = ind++;
+ cont[x] = 1;
+ S.push(x);
+
+ for (auto i : graph[x])
+ if (L[i] == -1) {
+ dfs(i);
+ low[x] = min(low[x], low[i]);
+ } else if (cont[i])
+ low[x] = min(low[x], L[i]);
+
+ if (low[x] == L[x]) {
+ int w;
+ ncomp++;
+
+ do {
+ w = S.top(); S.pop();
+ cont[w] = 0;
+ scc[ncomp].pb(w);
+ } while (w != x);
+ }
+}
+
+
+// Return number of SCCs
+int tarjan(int n) {
+ memset(L, -1, sizeof L);
+ ncomp = ind = 0;
+
+ for (int i = 0; i < n; ++i)
+ if (L[i] == -1)
+ dfs(i);
+
+ return ncomp;
+}
--
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