steal kactl code :3

content/graphs/HopcroftKarp.h

@@ -0,0 +1,34 @@
+/**
+ * Author: Adam Soltan
+ * Date: 2026-01-13
+ * License: CC0
+ * Description: Fast bipartite matching algorithm. Graph $g$ should be a list
+ * of neighbors of the left partition, and $r$ should be a vector full of
+ * $-1$'s of the same size as the right partition. Returns the size of
+ * the matching. $r[i]$ will be the match for vertex $i$ on the right side,
+ * or $-1$ if it's not matched.
+ * Time: O(E \sqrt{V})
+ * Status: stress-tested by MinimumVertexCover and tested on Library Checker
+ */
+#pragma once
+
+int hopcroftKarp(vector<vi>& g, vi& r) {
+	int n = sz(g), res = 0;
+	vi l(n, -1), q(n), d(n);
+	auto dfs = [&](auto f, int u) -> bool {
+		int t = exchange(d[u], 0) + 1;
+		for (int v : g[u])
+			if (r[v] == -1 || (d[r[v]] == t && f(f, r[v])))
+				return l[u] = v, r[v] = u, 1;
+		return 0;
+	};
+	for (int t = 0, f = 0;; t = f = 0, d.assign(n, 0)) {
+		rep(i,0,n) if (l[i] == -1) q[t++] = i, d[i] = 1;
+		rep(i,0,t) for (int v : g[q[i]]) {
+			if (r[v] == -1) f = 1;
+			else if (!d[r[v]]) d[r[v]] = d[q[i]] + 1, q[t++] = r[v];
+		}
+		if (!f) return res;
+		rep(i,0,n) if (l[i] == -1) res += dfs(dfs, i);
+	}
+}

content/graphs/chapter.tex

@@ -17,7 +17,7 @@ \section{Network flow}
 	\kactlimport{MatroidIntersection.h}
 
 \section{Matching}
-	\kactlimport{hopcroftKarp.h}
+	\kactlimport{HopcroftKarp.h}
 	\kactlimport{DFSMatching.h}
 	\kactlimport{MinimumVertexCover.h}
 	\kactlimport{WeightedMatching.h}