POJ 2375 强联通缩点+判断

#pragma comment(linker,"/STACK:102400000,102400000")
#include <iostream>
#include <string.h>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
#include <queue>
#include <stack>
#include <map>
#include <set>
using namespace std;
typedef long long ll;   //ŒÇµÃ±ØÒªµÄʱºòžÄ³ÉÎÞ·ûºÅ
const int maxn=250005;   //µãÊý
const int maxm=1000005;   //±ßÊý
const int INF=1000000000;
struct EdgeNode
{
int from;
int to;
int next;
}edge[maxm];
int head[maxn],cnt;
void add(int x,int y)
{
edge[cnt].from=x;edge[cnt].to=y;edge[cnt].next=head[x];head[x]=cnt++;
//printf("%d %d\n",x,y);
}

void init()
{
cnt=0;
memset(head,-1,sizeof(head));
}

int dfn[maxn],low[maxn],ins[maxn],cixu,scc_count,n,ru[maxn],chu[maxn],sd[maxn];
stack<int>S;

void dfs(int u)
{
int v,x;
dfn[u]=low[u]=++cixu;
S.push(u);
ins[u]=1;
for(int i=head[u];i!=-1;i=edge[i].next)
{
v=edge[i].to;
if(!dfn[v]){
dfs(v);
low[u]=min(low[u],low[v]);
}
else if(ins[v])            //Èç¹ûÒÑŸ­Ëѹý£¬²¢ÇÒÔÚÕ»ÀïÃ棬Èç¹û²»ÔÚÕ»ÀïÃ棬˵Ã÷žÃµãÊôÓÚÆäËûµÄÇ¿Á¬Íš·ÖÁ¿ÀïÃæ
low[u]=min(low[u],dfn[v]);   //ŽËŽŠlowŽúÌædfnÒ²ÊÇ¿ÉÒԵģ¬µ«ÊÇÔÚtarjanÇóÎÞÏòÍŒµÄʱºò²»ÄÜ
}
if(dfn[u]==low[u])          //±íÊŸuΪŽËÇ¿Á¬Íš·ÖÁ¿µÚÒ»žö±»·¢Ïֵĵ㣬ÊôÓÚžÃÇ¿Á¬Íš·ÖÁ¿µÄËùÓеÄÆäËûµã¶ŒÔÚÕ»ÖУ¬ËûµÄÉÏÃæ
{
scc_count++;
do
{
x=S.top();
S.pop();
sd[x]=scc_count;
ins[x]=0;
}while(x!=u);
}
}

void tarjan(int n)
{
for(int i=1;i<=n;i++)sd[i]=i;   //Ëõµã±êŒÇÊý×é
memset(ins,0,sizeof(ins));
memset(dfn,0,sizeof(dfn));
memset(low,0,sizeof(low));
cixu=scc_count=0;
for(int i=1;i<=n;i++)        //¿ÉÄÜËùžøµÄ͌Ϊ²»Á¬ÍšµÄÍŒ£¬·Ö¿é£¬ÒòŽËÐèÒª±éÀúËùÓеĵã
{
if(!dfn[i])
dfs(i);
}
}

void SD()
{
int x,y,len=cnt;
init();
memset(ru,0,sizeof(ru));
memset(chu,0,sizeof(chu));
for(int i=0;i<len;i++){
x=sd[edge[i].from]; y=sd[edge[i].to];
if(x==y)continue;
add(x,y);
chu[x]++; ru[y]++;
}
}

int mp[505][505],js[505][505],ans,m;
int d[5][3]={{-1,0},{1,0},{0,-1},{0,1}};
int yj(int x,int y)
{
if(x<1||x>m||y<1||y>n)return 1;
return 0;
}
void build()
{
init();
int i,j,k,x,y;
for(i=1;i<=m;i++){
for(j=1;j<=n;j++){
for(k=0;k<4;k++){
x=i+d[k][0];
y=j+d[k][1];
if(yj(x,y))continue;
if(mp[i][j]>=mp[x][y])add(js[i][j],js[x][y]);
}
}
}
}

int main()
{
//freopen("in.txt","r",stdin);
//freopen("out.txt","w",stdout);
int i,j,rds,cds;
while(~scanf("%d%d",&n,&m))
{
ans=0;
for(i=1;i<=m;i++){
for(j=1;j<=n;j++){
js[i][j]=++ans;
scanf("%d",&mp[i][j]);
}
}
build();
tarjan(ans);
SD();
rds=cds=0;
for(i=1;i<=scc_count;i++){
if(ru[i]==0)rds++;
if(chu[i]==0)cds++;
}
if(rds==cds&&rds==scc_count)printf("%d\n",rds-1);
else printf("%d\n",max(rds,cds));
}
return 0;
}