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vector<vector<int>> adj;
// pairs ist der gematchte Knoten oder -1
vector<int> pairs, dist, ptr;
bool bfs(int l) {
queue<int> q;
for(int i = 0; i < l; i++) {
if (pairs[i] < 0) {dist[i] = 0; q.push(i);}
else dist[i] = -1;
}
bool exist = false;
while(!q.empty()) {
int u = q.front(); q.pop();
for (int v : adj[u]) {
if (pairs[v] < 0) {exist = true; continue;}
if (dist[pairs[v]] < 0) {
dist[pairs[v]] = dist[u] + 1;
q.push(pairs[v]);
}}}
return exist;
}
bool dfs(int u) {
for (; ptr[u] < sz(adj[u]); ptr[u]++) {
int v = adj[u][ptr[u]];
if (pairs[v] < 0 ||
(dist[pairs[v]] > dist[u] && dfs(pairs[v]))) {
pairs[v] = u; pairs[u] = v;
return true;
}}
return false;
}
int hopcroft_karp(int l) { // l = #Knoten links
int ans = 0;
pairs.assign(sz(adj), -1);
dist.resize(l);
// Greedy Matching, optionale Beschleunigung.
for (int i = 0; i < l; i++) for (int w : adj[i])
if (pairs[w] < 0) {pairs[i] = w; pairs[w] = i; ans++; break;}
while(bfs(l)) {
ptr.assign(l, 0);
for(int i = 0; i < l; i++) {
if (pairs[i] < 0) ans += dfs(i);
}}
return ans;
}
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