From 9e85ecc322be50ceaaeb6d505b7dd79677790acd Mon Sep 17 00:00:00 2001
From: Bruno Freitas Tissei <bft15@inf.ufpr.br>
Date: Mon, 18 Feb 2019 10:56:43 -0300
Subject: [PATCH] Add prim algorithm
Signed-off-by: Bruno Freitas Tissei <bft15@inf.ufpr.br>
---
algorithms/graph/prim.cpp | 40 +++++++++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)
create mode 100644 algorithms/graph/prim.cpp
diff --git a/algorithms/graph/prim.cpp b/algorithms/graph/prim.cpp
new file mode 100644
index 0000000..1229061
--- /dev/null
+++ b/algorithms/graph/prim.cpp
@@ -0,0 +1,40 @@
+/**
+ * Prim
+ *
+ * Complexity (Time): O(m log m)
+ * Complexity (Space): O(n + m)
+ */
+
+bool cont[MAX];
+vector<ii> graph[MAX];
+
+// Returns value of MST of graph
+int prim() {
+ mset(cont, false);
+ cont[0] = true;
+
+ // Add negative values to pq in order to give priority
+ // to the edge with the smallest weight
+ priority_queue<ii> pq;
+ for (auto i : graph[0])
+ pq.push(ii(-i.se, -i.fi));
+
+ // At each step, connect vertex with smallest weight to the MST
+ int ans = 0;
+ while (!pq.empty()) {
+ ii front = pq.top(); pq.pop();
+ int u = -front.se;
+ int w = -front.fi;
+
+ if (!cont[u]) {
+ ans += w;
+ cont[u] = true;
+
+ for (auto i : graph[u])
+ if (!cont[i.fi])
+ pq.push(ii(-i.se, -i.fi));
+ }
+ }
+
+ return ans;
+}
--
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