-
Notifications
You must be signed in to change notification settings - Fork 11
/
kattis_dominos.cpp
96 lines (80 loc) · 2.51 KB
/
kattis_dominos.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
/* Kattis - dominos
SCC to DAG compression, count number of DAG nodes with 0 in-degree. This time, we choose to use
kosaraju just to spice things up.
Time: O(V + E), Mem: O(V + E)
*/
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
#define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
int n, e, u, v, t, num_scc;
vi adjlist[100009], adjlist_t[100009], scc_index, topo_arr, dfs_num;
bool scc_non_0_in_deg[100009]; // true if scc has a non zero degree
void kosaraju(int u, int pass){
dfs_num[u] = 1;
vi &neighbours = (pass == 1) ? adjlist[u] : adjlist_t[u];
for (auto v: neighbours){
if (dfs_num[v] == -1){
kosaraju(v, pass);
}
}
topo_arr.emplace_back(u);
//printf("u: %d, pass: %d, num_scc: %d\n", u, pass, num_scc);
if (pass == 2){
scc_index[u] = num_scc; // colour graph according to num_scc (0 index)
}
}
int main(){
fast_cin();
cin >> t;
for (int tc=0;tc<t;tc++){
cin >> n >> e;
for (int i=0;i<n;i++){
adjlist[i].clear();
adjlist_t[i].clear();
}
scc_index.assign(n, -1);
dfs_num.assign(n, -1);
topo_arr.clear();
num_scc = 0;
for(int i=0;i<n;i++)
scc_non_0_in_deg[i]= false;
for (int i=0;i<e; i++){
cin >> u >> v;
u--; v--;
adjlist[u].emplace_back(v);
adjlist_t[v].emplace_back(u);
}
for (int i=0;i<n;i++){
if (dfs_num[i] == -1){
kosaraju(i, 1);
}
}
// for (auto i: topo_arr){cout << i << " ";} cout << endl;
dfs_num.assign(n, -1);
for (int i=n-1; i>=0; i--){
if (dfs_num[topo_arr[i]] == -1){
kosaraju(topo_arr[i], 2);
num_scc++;
}
}
for (u = 0; u<n; u++){
for (auto v: adjlist[u]){
if (scc_index[v] == scc_index[u])continue;
//printf("u: %d, v: %d\n", u, v);
scc_non_0_in_deg[scc_index[v]] = true;
}
}
//for (int i=0; i<n; i++){cout << scc_index[i] << " ";} cout << endl;
int ans = 0;
for (int i=0;i<num_scc;i++){
if (scc_non_0_in_deg[i] == false)ans++;
}
cout << ans << endl;
}
return 0;
}