POJ 2375

  1 #include <cstdio> 
  2 #include <iostream> 
  3 #include <cstring>  
  4 #include <cctype>  
  5 #include <algorithm>  
  6 #define LL unsigned __int64
  7 using namespace std; 
  8 
  9 const int N= 250050;
 10 
 11 struct Edge{
 12     int u,v;
 13     int next;
 14 }edge[N*4];
 15 int tot,index;
 16 int head[N],dfn[N],low[N],stack[N],st;
 17 int outdegree[N],indegree[N];
 18 int belong[N],beg;
 19 bool instack[N];
 20 int map[510][510];
 21 
 22 int dir[4][2]={
 23     {0,1},
 24     {0,-1},
 25     {1,0},
 26     {-1,0}
 27 };
 28 
 29 void addedge(int u,int v){
 30     edge[tot].u=u;
 31     edge[tot].v=v;
 32     edge[tot].next=head[u];
 33     head[u]=tot++;
 34 }
 35 
 36 void Tarjan(int u) {
 37     dfn[u]=low[u]=++index;
 38     stack[st++]=u;
 39     instack[u]=true;
 40     for(int e=head[u];e!=-1;e=edge[e].next){
 41         int v=edge[e].v;
 42         if (dfn[v]==-1) {
 43             Tarjan(v) ;
 44             low[u] = min(low[u], low[v]) ;
 45         }
 46         else if (instack[v]) {
 47             low[u] = min(low[u], dfn[v]) ;
 48         }
 49     }
 50     int v;
 51     if (dfn[u] == low[u]) { 
 52         beg++;
 53         outdegree[beg]=indegree[beg]=0;
 54         do{
 55             v=stack[--st];
 56             belong[v]=beg;
 57             instack[v]=false;
 58         }while(u!= v);
 59     } 
 60 } 
 61 
 62 
 63 bool ok(int i,int j,int x,int y){
 64     if(i>=0&&i<x&&j>=0&&j<y) return true;
 65     return false;
 66 }
 67 
 68 int main(){
 69     int x,y;
 70     while(scanf("%d%d",&y,&x)!=EOF){
 71         for(int i=0;i<x;i++){
 72             for(int j=0;j<y;j++)
 73             scanf("%d",&map[i][j]);
 74         }
 75         
 76         tot=index=st=beg=0;
 77         int u,v,tx,ty;
 78         int spoint=x*y;
 79         for(int i=0;i<=spoint;i++){
 80             head[i]=dfn[i]=low[i]=belong[i]=-1;
 81             instack[i]=false;
 82         }
 83         
 84         for(int i=0;i<x;i++){
 85             for(int j=0;j<y;j++){
 86                 u=i*y+j;
 87                 for(int k=0;k<4;k++){
 88                     tx=i+dir[k][0];
 89                     ty=j+dir[k][1];
 90                     if(ok(tx,ty,x,y)){
 91                         if(map[tx][ty]<=map[i][j]){
 92                             v=tx*y+ty;
 93                             addedge(u,v);
 94                         }
 95                     }
 96                 }
 97             }
 98         }
 99         
100         for(int i=0;i<spoint;i++){
101             if(dfn[i]==-1){
102                 Tarjan(i);
103             }
104         }
105         
106         for(int i=0;i<spoint;i++){
107             u=i;
108             for(int e=head[u];e!=-1;e=edge[e].next){
109                 v=edge[e].v;
110                 if(belong[u]!=belong[v]){
111                     outdegree[belong[u]]++;
112                     indegree[belong[v]]++;
113                 }
114             }
115         }
116         
117         int ou=0,in=0;
118         if(beg==1){
119             puts("0");
120             continue;
121         }
122         for(int i=1;i<=beg;i++){
123             if(outdegree[i]==0){
124                 ou++;
125             }
126             if(indegree[i]==0)
127             in++;
128         }
129         
130         printf("%d\n",max(ou,in));
131     }
132     return 0;
133 }