1 files changed, 32 insertions, 0 deletions
diff --git a/graph/LCA_sparse.cpp b/graph/LCA_sparse.cpp
new file mode 100644
index 0000000..2a38528
--- /dev/null
+++ b/graph/LCA_sparse.cpp
@@ -0,0 +1,32 @@
+struct LCA {
+	vector<ll> depth;
+	vector<int> visited, first;
+	int idx;
+	SparseTable st; //sparse table von oben
+
+	void init(vector<vector<int>>& g, int root) {
+		depth.assign(2 * sz(g), 0);
+		visited.assign(2 * sz(g), -1);
+		first.assign(sz(g), 2 * sz(g));
+		idx = 0;
+		visit(g, root);
+		st.init(&depth);
+	}
+
+	void visit(vector<vector<int>>& g, int v, ll d=0, int p=-1) {
+		visited[idx] = v, depth[idx] = d;
+		first[v] = min(idx, first[v]), idx++;
+
+		for (int w : g[v]) {
+			if (first[w] == 2 * sz(g)) {
+				visit(g, w, d + 1, v);
+				visited[idx] = v, depth[idx] = d, idx++;
+	}}}
+
+	int getLCA(int a, int b) {
+		if (first[a] > first[b]) swap(a, b);
+		return visited[st.queryIdempotent(first[a], first[b] + 1)];
+	}
+
+	ll getDepth(int a) {eturn depth[first[a]];}
+};