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| #include <array>
#include <iostream>
#include <queue>
#include <vector>
using namespace std;
const int N = 1e4 + 5;
const int INF = 0x7f7f7f7f;
struct Graph {
struct Node {
int v, w, nxt;
};
std::vector<int> head;
std::vector<Node> edge;
Graph() {
}
Graph(int n) : head(n + 1, -1){};
void resize(int n) {
head.assign(n + 1, -1);
}
void add(int u, int v, int w) {
if (head.size() < u) {
head.reserve(u * 2);
}
edge.emplace_back(Node{v, w, head[u]});
head[u] = edge.size() - 1;
}
void add_flow(int u, int v, int w) {
add(u, v, w);
add(v, u, 0);
}
};
namespace NetworkFlow {
std::vector<int> level;
bool bfs(int S, int T, const Graph &G) {
level.assign(G.head.size(), 0);
level[S] = 1;
std::queue<int> q;
q.push(S);
while (!q.empty()) {
int now = q.front();
q.pop();
for (int i = G.head[now]; ~i; i = G.edge[i].nxt) {
int v = G.edge[i].v;
if (!level[v] && G.edge[i].w) {
level[v] = level[now] + 1;
q.push(v);
}
}
}
return level[T];
}
std::vector<int> cur;
int dfs(int x, int T, int maxflow, Graph &G) {
if (x == T) {
return maxflow;
}
int res = 0;
for (int i = cur[x]; ~i && res < maxflow; i = G.edge[i].nxt) {
cur[x] = i;
int v = G.edge[i].v;
if (G.edge[i].w && level[v] == level[x] + 1) {
int x = dfs(v, T, std::min(G.edge[i].w, maxflow - res), G);
if (x) {
G.edge[i].w -= x;
G.edge[i ^ 1].w += x;
res += x;
}
}
}
if (res < maxflow) {
level[x] = -1;
}
return res;
}
int MaxFlow(const int S, const int T, const Graph &G) {
cur.resize(G.head.size());
level.resize(G.head.size());
Graph tmpG = G;
int res = 0;
while (bfs(S, T, tmpG)) {
cur.assign(tmpG.head.begin(), tmpG.head.end());
int x;
while (x = dfs(S, T, INF, tmpG)) {
res += x;
}
}
return res;
}
}
int S, T;
Graph G;
array<int, N * 20> id, col;
int idcnt;
namespace SegmentTree {
using namespace NetworkFlow;
#define ls(x) (x * 2)
#define rs(x) (x * 2 + 1)
void build(int rt, int l, int r) {
if (l == r) {
id[rt] = l;
G.add_flow(l, T, 1);
col[rt] = l;
return;
}
id[rt] = col[rt] = ++idcnt;
int mid = (l + r) / 2;
build(ls(rt), l, mid);
build(rs(rt), mid + 1, r);
G.add_flow(col[rt], col[ls(rt)], INF);
G.add_flow(col[rt], col[rs(rt)], INF);
}
void update(int rt, int l, int r, int L, int R, int v) {
if (L <= l && r <= R) {
if (v) {
id[rt] = col[rt];
} else {
id[rt] = -1;
}
return;
}
int mid = (l + r) / 2;
id[rt] = ++idcnt;
if (L <= mid) {
update(ls(rt), l, mid, L, R, v);
}
if (mid < R) {
update(rs(rt), mid + 1, r, L, R, v);
}
if (id[ls(rt)] != -1) {
G.add_flow(id[rt], id[ls(rt)], INF);
}
if (id[rs(rt)] != -1) {
G.add_flow(id[rt], id[rs(rt)], INF);
}
}
#undef ls
#undef rs
}
int n, q;
vector<pair<int, int>> st[N], ed[N];
int main() {
cin >> n >> q;
G.resize(n * 80);
S = idcnt = n + 1;
T = S + 1;
for (int i = 1; i <= q; i++) {
int x1, y1, x2, y2;
cin >> x1 >> y1 >> x2 >> y2;
st[x1].emplace_back(make_pair(y1, y2));
ed[x2 + 1].emplace_back(make_pair(y1, y2));
}
SegmentTree::build(1, 1, n);
for (int i = 1; i <= n; i++) {
for (auto v : ed[i]) {
SegmentTree::update(1, 1, n, v.first, v.second, 1);
}
for (auto v : st[i]) {
SegmentTree::update(1, 1, n, v.first, v.second, 0);
}
if (id[1] != -1)
G.add_flow(S, id[1], 1);
}
cout << NetworkFlow::MaxFlow(S, T, G);
return 0;
}
|