Hoj 2632 Blanks in a Table

题目链接：http://acm.hit.edu.cn/hoj/problem/view?id=2632

题意：

设a代表空，a'代表非空。

b代表空，b'代表非空。

那么：

有n个条件要求a和b不可同时为空，则：a->b',b->a'

有p个条件要求a和b至少有一个为空，则：a'->b,b'->a

#include <stdio.h>#include <stdlib.h>#include <string.h>#include <math.h>#include <stack>#include <queue>#include <algorithm>#include <iostream>using namespace std;#define Maxn (1005 * 2)#define Maxm (2005 * 4)struct Edge{int a,b;}edge[Maxm];int first[Maxn],next[Maxm];int total;//scc相关int sccno[Maxn];bool instack[Maxn];int dfn[Maxn];int low[Maxn];int dfs_clock;int scc_cnt;stack <int> st;//2sat相关void addEdge(int a,int b){edge[total].a = a,edge[total].b = b;next[total] = first[a];first[a] = total++;}void init(){total = 0;memset(first,-1,sizeof(first));}void tarjan(int u){  dfn[u] = low[u] = ++dfs_clock;  st.push(u);  instack[u] = true;  for(int i=first[u];i!=-1;i=next[i])  {    int v = edge[i].b;    if(!dfn[v])    {      tarjan(v);      low[u] = min(low[u],low[v]);    }    else if(instack[v])    {      low[u] = min(low[u],dfn[v]);    }  }  if(dfn[u] == low[u])  {    scc_cnt++;    while(1)    {      int v = st.top();      st.pop();      instack[v] = false;      sccno[v] = scc_cnt;      if(u == v) break;    }  }}void find_scc(int start,int n){scc_cnt = dfs_clock = 0;memset(dfn,0,sizeof(dfn));memset(low,0,sizeof(low));  memset(instack,false,sizeof(instack));  while(!st.empty())  {    st.pop();  }  for(int i=start;i<=n;i++)  {    if(!dfn[i]) tarjan(i);  }}bool twoSet(int start,int n,int add){find_scc(start,n);for(int i=start;i<=n;i++){int temp;if(i>add) temp = i-add;else temp = i+add;if(sccno[i] == sccno[temp]) return false;}return true;}int main(){#ifndef ONLINE_JUDGEfreopen("in.txt","r",stdin);#endifint n,m,p;int a,b;while(scanf(" %d %d %d",&m,&n,&p)!=EOF){init();//不可同时为空for(int i=0;i<n;i++){scanf(" %d %d",&a,&b);addEdge(a,b+m);addEdge(b,a+m);}//至少有一个为空for(int i=0;i<p;i++){scanf(" %d %d",&a,&b);addEdge(b+m,a);addEdge(a+m,b);}if(!twoSet(1,2*m,m)){puts("No");continue;}puts("Yes");}return 0;}