## poj 3207 Ikki’s Story IV – Panda’s Trick

2019年11月08日 算法 ⁄ 共 2501字 ⁄ 字号 评论关闭

2-SAT

```#include<iostream>
#include<map>
#include<string>
#include<cstring>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<queue>
#include<vector>
#include<algorithm>
using namespace std;
const int MAXN = 510;
struct twosat
{
int n,c;
vector<int> g[MAXN<<1];
bool mark[MAXN<<1];
int s[MAXN<<1];

bool dfs(int x)
{
int i;
if (mark[x^1])
return 0;
if (mark[x])
return 1;
mark[x] = 1;
s[c++] = x;
for (i = 0; i < g[x].size(); i++)
if (!dfs(g[x][i]))
return 0;
return 1;
}

void init(int n)
{
int i,t=n<<1;
this->n = n;
for (i = 0; i < t; i++)
g[i].clear();
memset(mark, 0, sizeof(mark));
}

void add_clause(int x, int xval, int y, int yval)
{
x = x * 2 + xval;
y = y * 2 + yval;
g[x^1].push_back(y);
g[y^1].push_back(x);
}

bool solve()
{
int i,t=n<<1;
for (i = 0; i < t; i += 2)
if (!mark[i] && !mark[i + 1])
{
c = 0;
if (!dfs(i))
{
while (c > 0)
mark[s[--c]] =0;
if (!dfs(i + 1))
return 0;
}
}
return 1;
}
}ender;
struct seg
{
int s,e;
}in;
bool iscross(seg a,seg b,int flag1,int flag2)
{
if(flag1!=flag2)
return 0;
if(a.s<b.s&&b.s<a.e&&(b.e<a.s||b.e>a.e))
return 1;
if(b.s<a.s&&a.s<b.e&&(a.e<b.s||a.e>b.e))
return 1;
return 0;
}
int main()
{
int i,j,n,m,x,y;
cin>>n>>m;
for(i=0;i<m;i++)
{
cin>>in[i].s>>in[i].e;
if(in[i].s>in[i].e)
swap(in[i].s,in[i].e);
}
ender.init(m);
for(i=0;i<m;i++)
for(j=i+1;j<m;j++)
for(x=0;x<2;x++)
for(y=0;y<2;y++)
if(iscross(in[i],in[j],x,y))
if(ender.solve())
cout<<"panda is telling the truth..."<<endl;
else
cout<<"the evil panda is lying again"<<endl;
return 0;
}```

Ikki's Story IV - Panda's Trick
 Time Limit: 1000MS Memory Limit: 131072K Total Submissions: 8142 Accepted: 2993

Description

liympanda, one of Ikki’s friend, likes playing games with Ikki. Today after minesweeping with Ikki and winning so many times, he is tired of such easy games and wants to play another game with Ikki.

liympanda has a magic circle and he puts it on a plane, there are n points on its boundary in circular border: 0, 1, 2, …,
n − 1. Evil panda claims that he is connecting m pairs of points. To connect two points, liympanda either places the link entirely inside the circle or entirely outside the circle. Now liympanda tells Ikki no two links touch inside/outside the circle,
except on the boundary. He wants Ikki to figure out whether this is possible…

Despaired at the minesweeping game just played, Ikki is totally at a loss, so he decides to write a program to help him.

Input

The input contains exactly one test case.

In the test case there will be a line consisting of of two integers: n and
m (n ≤ 1,000, m ≤ 500). The following m lines each contain two integers
ai and bi, which denote the endpoints of the
ith wire. Every point will have at most one link.

Output

Output a line, either “`panda is telling the truth...`” or “`the evil panda is lying again`”.

Sample Input

```4 2
0 1
3 2```

Sample Output

`panda is telling the truth...`

Source