1 files changed, 18 insertions, 0 deletions
diff --git a/content/graph/havelHakimi.cpp b/content/graph/havelHakimi.cpp
new file mode 100644
index 0000000..ac4d67d
--- /dev/null
+++ b/content/graph/havelHakimi.cpp
@@ -0,0 +1,18 @@
+vector<vector<int>> havelHakimi(const vector<int>& deg) {
+	priority_queue<pair<int, int>> pq;
+	for (int i = 0; i < sz(deg); i++) {
+		if (deg[i] > 0) pq.push({deg[i], i});
+	}
+	vector<vector<int>> adj(sz(deg));
+	while (!pq.empty()) {
+		auto [degV, v] = pq.top(); pq.pop();
+		if (sz(pq) < degV) return {}; //impossible
+		vector<pair<int, int>> todo(degV);
+		for (auto& e : todo) e = pq.top(), pq.pop();
+		for (auto [degU, u] : todo) {
+			adj[v].push_back(u);
+			adj[u].push_back(v);
+			if (degU > 1) pq.push({degU - 1, u});
+	}}
+	return adj;
+}