Hdu_3836 equivalent set (Trajan strongly connected component contraction point)

Calculate the strongly connected component and reduce the point. Obtain the Dag of The New Graph and calculate the max value in the DAG (number of points with an inbound degree of 0 and number of points with an outbound degree of 0 );

Slag code:

View code

1 # include <iostream>
2 # include <cstdio>
3 # include <cstring>
4 # include <stack>
5
6 using namespace STD;
7
8 const int n = 20010;
9 const int M = 50010;
10
11 struct node {
12 INT;
13 node * next;
14} * First [m];
15
16 int head [N], blong [N];
17 int dfn [N], low [N];
18 int in [N], out [N];
19 int CNT, T, IND;
20 bool vis [N];
21
22 stack <int> S;
23
24 void Init (){
25 memset (Head, 0, sizeof (head ));
26 memset (blong, 0, sizeof (blong ));
27 memset (dfn, 0, sizeof (dfn ));
28 memset (low, 0, sizeof (low ));
29 memset (Out, 0, sizeof (out ));
30 memset (VIS, 0, sizeof (VIS ));
31 memset (in, 0, sizeof (in ));
32 memset (first, null, sizeof (first ));
33
34 t = 1; ind = CNT = 0;
35}
36
37 void add (int u, int v ){
38 node * TMP = new node;
39 TMP-> to = V;
40 TMP-> next = first [u];
41 First [u] = TMP;
42}
43
44 void Tarjan (int u ){
45 int V;
46 vis [u] = true;
47 s. Push (U );
48 low [u] = dfn [u] = ++ ind;
49 for (node * Pos = first [u]; pos! = NULL; Pos = pos-> next ){
50 V = pos->;
51 if (! Dfn [v]) {
52 Tarjan (v );
53 low [u] = min (low [v], low [u]);
54} else if (vis [v]) {
55 low [u] = min (low [u], low [v]);
56}
57}
58 If (low [u] = dfn [u]) {
59 CNT ++;
60 do {
61 V = S. Top (); S. Pop ();
62 blong [v] = CNT;
63 vis [v] = false;
64 // printf ("% d \ n", V, CNT );
65} while (V! = U );
66}
67}
68
69 int main (){
70 // freopen ("data. In", "r", stdin );
71
72 int n, m, A, B, I;
73 while (~ Scanf ("% d", & N, & M )){
74 Init ();
75 for (I = 1; I <= m; I ++ ){
76 scanf ("% d", & A, & B );
77 add (B, );
78}
79
80 for (I = 1; I <= N; I ++ ){
81 If (! Dfn [I]) Tarjan (I );
82}
83 If (CNT = 1) {printf ("0 \ n"); continue;} // note that when only one strongly connected component is used
84 for (I = 1; I <= N; I ++ ){
85 for (node * P = first [I]; P! = NULL; P = p-> next ){
86 A = p->;
87 If (blong [I]! = Blong [a]) {
88 in [blong [a] ++;
89 out [blong [I] ++;
90}
91}
92}
93 a = B = 0;
94 for (I = 1; I <= CNT; I ++ ){
95 If (! In [I]) A ++;
96 If (! Out [I]) B ++;
97}
98 printf ("% d \ n", max (a, B ));
99}
100 return 0;
101}