Skip to content

Commit f93a3b5

Browse files
yosupo06yosupo06
committed
optimize mcf
1 parent 637afb8 commit f93a3b5

File tree

4 files changed

+153
-87
lines changed

4 files changed

+153
-87
lines changed

‎atcoder/internal_csr

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
#include "atcoder/internal_csr.hpp"

‎atcoder/internal_csr.hpp

Lines changed: 33 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,33 @@
1+
#ifndef ATCODER_INTERNAL_CSR_HPP
2+
#define ATCODER_INTERNAL_CSR_HPP 1
3+
4+
#include <algorithm>
5+
#include <utility>
6+
#include <vector>
7+
8+
namespace atcoder {
9+
namespace internal {
10+
11+
template <class E> struct csr {
12+
std::vector<int> start;
13+
std::vector<E> elist;
14+
csr(int n, const std::vector<std::pair<int, E>>& edges)
15+
: start(n + 1), elist(edges.size()) {
16+
for (auto e : edges) {
17+
start[e.first + 1]++;
18+
}
19+
for (int i = 1; i <= n; i++) {
20+
start[i] += start[i - 1];
21+
}
22+
auto counter = start;
23+
for (auto e : edges) {
24+
elist[counter[e.first]++] = e.second;
25+
}
26+
}
27+
};
28+
29+
} // namespace internal
30+
31+
} // namespace atcoder
32+
33+
#endif // ATCODER_INTERNAL_CSR_HPP

‎atcoder/internal_scc.hpp

Lines changed: 2 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -5,27 +5,11 @@
55
#include <utility>
66
#include <vector>
77

8+
#include "atcoder/internal_csr"
9+
810
namespace atcoder {
911
namespace internal {
1012

11-
template <class E> struct csr {
12-
std::vector<int> start;
13-
std::vector<E> elist;
14-
csr(int n, const std::vector<std::pair<int, E>>& edges)
15-
: start(n + 1), elist(edges.size()) {
16-
for (auto e : edges) {
17-
start[e.first + 1]++;
18-
}
19-
for (int i = 1; i <= n; i++) {
20-
start[i] += start[i - 1];
21-
}
22-
auto counter = start;
23-
for (auto e : edges) {
24-
elist[counter[e.first]++] = e.second;
25-
}
26-
}
27-
};
28-
2913
// Reference:
3014
// R. Tarjan,
3115
// Depth-First Search and Linear Graph Algorithms

‎atcoder/mincostflow.hpp

Lines changed: 117 additions & 69 deletions
Original file line numberDiff line numberDiff line change
@@ -7,25 +7,23 @@
77
#include <queue>
88
#include <vector>
99

10+
#include "atcoder/internal_csr"
11+
#include "atcoder/internal_queue"
12+
1013
namespace atcoder {
1114

1215
template <class Cap, class Cost> struct mcf_graph {
1316
public:
1417
mcf_graph() {}
15-
mcf_graph(int n) : _n(n), g(n) {}
18+
mcf_graph(int n) : _n(n) {}
1619

1720
int add_edge(int from, int to, Cap cap, Cost cost) {
1821
assert(0 <= from && from < _n);
1922
assert(0 <= to && to < _n);
2023
assert(0 <= cap);
2124
assert(0 <= cost);
22-
int m = int(pos.size());
23-
pos.push_back({from, int(g[from].size())});
24-
int from_id = int(g[from].size());
25-
int to_id = int(g[to].size());
26-
if (from == to) to_id++;
27-
g[from].push_back(_edge{to, to_id, cap, cost});
28-
g[to].push_back(_edge{from, from_id, 0, -cost});
25+
int m = int(_edges.size());
26+
_edges.push_back({from, to, cap, 0, cost});
2927
return m;
3028
}
3129

@@ -36,28 +34,17 @@ template <class Cap, class Cost> struct mcf_graph {
3634
};
3735

3836
edge get_edge(int i) {
39-
int m = int(pos.size());
37+
int m = int(_edges.size());
4038
assert(0 <= i && i < m);
41-
auto _e = g[pos[i].first][pos[i].second];
42-
auto _re = g[_e.to][_e.rev];
43-
return edge{
44-
pos[i].first, _e.to, _e.cap + _re.cap, _re.cap, _e.cost,
45-
};
46-
}
47-
std::vector<edge> edges() {
48-
int m = int(pos.size());
49-
std::vector<edge> result(m);
50-
for (int i = 0; i < m; i++) {
51-
result[i] = get_edge(i);
52-
}
53-
return result;
39+
return _edges[i];
5440
}
41+
std::vector<edge> edges() { return _edges; }
5542

5643
std::pair<Cap, Cost> flow(int s, int t) {
5744
return flow(s, t, std::numeric_limits<Cap>::max());
5845
}
5946
std::pair<Cap, Cost> flow(int s, int t, Cap flow_limit) {
60-
return slope(s, t, flow_limit).back();
47+
return slope(s, t, flow_limit).back();
6148
}
6249
std::vector<std::pair<Cap, Cost>> slope(int s, int t) {
6350
return slope(s, t, std::numeric_limits<Cap>::max());
@@ -66,49 +53,122 @@ template <class Cap, class Cost> struct mcf_graph {
6653
assert(0 <= s && s < _n);
6754
assert(0 <= t && t < _n);
6855
assert(s != t);
56+
57+
int m = int(_edges.size());
58+
std::vector<int> edge_idx(m);
59+
60+
auto g = [&]() {
61+
std::vector<int> degree(_n), redge_idx(m);
62+
std::vector<std::pair<int, _edge>> elist;
63+
elist.reserve(2 * m);
64+
for (int i = 0; i < m; i++) {
65+
auto e = _edges[i];
66+
edge_idx[i] = degree[e.from]++;
67+
redge_idx[i] = degree[e.to]++;
68+
elist.push_back({e.from, {e.to, -1, e.cap - e.flow, e.cost}});
69+
elist.push_back({e.to, {e.from, -1, e.flow, -e.cost}});
70+
}
71+
auto _g = internal::csr<_edge>(_n, elist);
72+
for (int i = 0; i < m; i++) {
73+
auto e = _edges[i];
74+
edge_idx[i] += _g.start[e.from];
75+
redge_idx[i] += _g.start[e.to];
76+
_g.elist[edge_idx[i]].rev = redge_idx[i];
77+
_g.elist[redge_idx[i]].rev = edge_idx[i];
78+
}
79+
return _g;
80+
}();
81+
82+
auto result = slope(g, s, t, flow_limit);
83+
84+
for (int i = 0; i < m; i++) {
85+
auto e = g.elist[edge_idx[i]];
86+
_edges[i].flow = _edges[i].cap - e.cap;
87+
}
88+
89+
return result;
90+
}
91+
92+
private:
93+
int _n;
94+
std::vector<edge> _edges;
95+
96+
// inside edge
97+
struct _edge {
98+
int to, rev;
99+
Cap cap;
100+
Cost cost;
101+
};
102+
103+
std::vector<std::pair<Cap, Cost>> slope(internal::csr<_edge>& g,
104+
int s,
105+
int t,
106+
Cap flow_limit) {
69107
// variants (C = maxcost):
70108
// -(n-1)C <= dual[s] <= dual[i] <= dual[t] = 0
71109
// reduced cost (= e.cost + dual[e.from] - dual[e.to]) >= 0 for all edge
72-
std::vector<Cost> dual(_n, 0), dist(_n);
73-
std::vector<int> pv(_n), pe(_n);
110+
111+
// dual_dist[i] = (dual[i], dist[i])
112+
std::vector<std::pair<Cost, Cost>> dual_dist(_n);
113+
std::vector<int> prev_e(_n);
74114
std::vector<bool> vis(_n);
75115
struct Q {
76116
Cost key;
77117
int to;
78118
bool operator<(Q r) const { return key > r.key; }
79119
};
120+
std::vector<int> que_min;
80121
std::vector<Q> que;
81122
auto dual_ref = [&]() {
82-
std::fill(dist.begin(), dist.end(),
83-
std::numeric_limits<Cost>::max());
123+
for (int i = 0; i < _n; i++) {
124+
dual_dist[i].second = std::numeric_limits<Cost>::max();
125+
}
84126
std::fill(vis.begin(), vis.end(), false);
127+
que_min.clear();
85128
que.clear();
86129

87-
dist[s] = 0;
88-
que.push_back(Q{0, s});
89-
std::push_heap(que.begin(), que.end());
90-
while (!que.empty()) {
91-
int v = que.front().to;
92-
std::pop_heap(que.begin(), que.end());
93-
que.pop_back();
130+
// que[0..heap_r) was heapified
131+
size_t heap_r = 0;
132+
133+
dual_dist[s].second = 0;
134+
que_min.push_back(s);
135+
while (!que_min.empty() || !que.empty()) {
136+
int v;
137+
if (!que_min.empty()) {
138+
v = que_min.back();
139+
que_min.pop_back();
140+
} else {
141+
while (heap_r < que.size()) {
142+
heap_r++;
143+
std::push_heap(que.begin(), que.begin() + heap_r);
144+
}
145+
v = que.front().to;
146+
std::pop_heap(que.begin(), que.end());
147+
que.pop_back();
148+
heap_r--;
149+
}
94150
if (vis[v]) continue;
95151
vis[v] = true;
96152
if (v == t) break;
97153
// dist[v] = shortest(s, v) + dual[s] - dual[v]
98154
// dist[v] >= 0 (all reduced cost are positive)
99155
// dist[v] <= (n-1)C
100-
for (int i = 0; i < int(g[v].size()); i++) {
101-
auto e = g[v][i];
102-
if (vis[e.to] || !e.cap) continue;
156+
Cost dual_v = dual_dist[v].first, dist_v = dual_dist[v].second;
157+
for (int i = g.start[v]; i < g.start[v + 1]; i++) {
158+
auto e = g.elist[i];
159+
if (!e.cap) continue;
103160
// |-dual[e.to] + dual[v]| <= (n-1)C
104161
// cost <= C - -(n-1)C + 0 = nC
105-
Cost cost = e.cost - dual[e.to] + dual[v];
106-
if (dist[e.to] - dist[v] > cost) {
107-
dist[e.to] = dist[v] + cost;
108-
pv[e.to] = v;
109-
pe[e.to] = i;
110-
que.push_back(Q{dist[e.to], e.to});
111-
std::push_heap(que.begin(), que.end());
162+
Cost cost = e.cost - dual_dist[e.to].first + dual_v;
163+
if (dual_dist[e.to].second - dist_v > cost) {
164+
Cost dist_to = dist_v + cost;
165+
dual_dist[e.to].second = dist_to;
166+
prev_e[e.to] = e.rev;
167+
if (dist_to == dist_v) {
168+
que_min.push_back(e.to);
169+
} else {
170+
que.push_back(Q{dist_to, e.to});
171+
}
112172
}
113173
}
114174
}
@@ -119,29 +179,29 @@ template <class Cap, class Cost> struct mcf_graph {
119179
for (int v = 0; v < _n; v++) {
120180
if (!vis[v]) continue;
121181
// dual[v] = dual[v] - dist[t] + dist[v]
122-
// = dual[v] - (shortest(s, t) + dual[s] - dual[t]) + (shortest(s, v) + dual[s] - dual[v])
123-
// = - shortest(s, t) + dual[t] + shortest(s, v)
124-
// = shortest(s, v) - shortest(s, t) >= 0 - (n-1)C
125-
dual[v] -= dist[t] - dist[v];
182+
// = dual[v] - (shortest(s, t) + dual[s] - dual[t]) +
183+
// (shortest(s, v) + dual[s] - dual[v]) = - shortest(s,
184+
// t) + dual[t] + shortest(s, v) = shortest(s, v) -
185+
// shortest(s, t) >= 0 - (n-1)C
186+
dual_dist[v].first -= dual_dist[t].second - dual_dist[v].second;
126187
}
127188
return true;
128189
};
129190
Cap flow = 0;
130191
Cost cost = 0, prev_cost_per_flow = -1;
131-
std::vector<std::pair<Cap, Cost>> result;
132-
result.push_back({flow, cost});
192+
std::vector<std::pair<Cap, Cost>> result = {{Cap(0), Cost(0)}};
133193
while (flow < flow_limit) {
134194
if (!dual_ref()) break;
135195
Cap c = flow_limit - flow;
136-
for (int v = t; v != s; v = pv[v]) {
137-
c = std::min(c, g[pv[v]][pe[v]].cap);
196+
for (int v = t; v != s; v = g.elist[prev_e[v]].to) {
197+
c = std::min(c, g.elist[g.elist[prev_e[v]].rev].cap);
138198
}
139-
for (int v = t; v != s; v = pv[v]) {
140-
auto& e = g[pv[v]][pe[v]];
141-
e.cap -= c;
142-
g[v][e.rev].cap += c;
199+
for (int v = t; v != s; v = g.elist[prev_e[v]].to) {
200+
auto& e = g.elist[prev_e[v]];
201+
e.cap += c;
202+
g.elist[e.rev].cap -= c;
143203
}
144-
Cost d = -dual[s];
204+
Cost d = -dual_dist[s].first;
145205
flow += c;
146206
cost += c * d;
147207
if (prev_cost_per_flow == d) {
@@ -152,18 +212,6 @@ template <class Cap, class Cost> struct mcf_graph {
152212
}
153213
return result;
154214
}
155-
156-
private:
157-
int _n;
158-
159-
struct _edge {
160-
int to, rev;
161-
Cap cap;
162-
Cost cost;
163-
};
164-
165-
std::vector<std::pair<int, int>> pos;
166-
std::vector<std::vector<_edge>> g;
167215
};
168216

169217
} // namespace atcoder

0 commit comments

Comments
 (0)