题意:
有N个炸弹..每个炸弹有两个位置可以选择..把炸弹放到其中一个地方去...炸弹的爆炸范围是其为圆心的圆...两个炸弹不能有攻击范围上的重合..问要满足条件..炸弹爆炸范围的半径最长能是多少...
题解:
每个炸弹看成一类..其在两个中比选一个..符合2-sat的构图条件....那么就二分枚举炸弹的爆炸范围..枚举相互是否干扰来做边构造2-sat模型...tarjan来判断是否合法..
题目不难..但是我2B了...在初始化vector时..for (i=0;i<(n<<1);i++) T[i].clear() 写成了for (i=0;i<(1<<n);i++) T[i].clear()...搞得我查了好久的错误..还写了几个版本的代码..这道题不好自己出数据..搞得很郁闷..最后怀疑是vector使用的问题..就索性写了个链表..结果就A了~~再反过头来看..发现了错误的根源...弱啊......
Program-----链表存图..整个程序int型计算..结果再开方除2输出
#include<iostream>
#include<stdio.h>
#include<string.h>
#include<cmath>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<algorithm>
#define ll long long
#define oo 1000000007
#define pi acos(-1.0)
#define MAXN 205
#define MAXM 100005
using namespace std;
struct node
{
int x0,y0,x1,y1;
}b[MAXN];
struct LINE
{
int x,y,next;
}line[MAXM];
int Lnum,_next[MAXN],dfn[MAXN],low[MAXN],tp[MAXN],tpnum,DfsIndex,arc[MAXN][MAXN];
bool instack[MAXN];
stack<int> mystack;
int dis(int x0,int y0,int x1,int y1)
{
return (x0-x1)*(x0-x1)+(y0-y1)*(y0-y1);
}
void addline(int x,int y)
{
line[++Lnum].next=_next[x],_next[x]=Lnum;
line[Lnum].x=x,line[Lnum].y=y;
}
void tarjan(int x)
{
int y,k;
dfn[x]=low[x]=++DfsIndex;
instack[x]=true;
mystack.push(x);
for (k=_next[x];k;k=line[k].next)
{
y=line[k].y;
if (!dfn[y])
{
tarjan(y);
low[x]=min(low[x],low[y]);
}else
if (instack[y]) low[x]=min(low[x],dfn[y]);
}
if (dfn[x]==low[x])
{
tpnum++;
do
{
x=mystack.top();
mystack.pop();
instack[x]=false;
tp[x]=tpnum;
}while (dfn[x]!=low[x]);
}
return;
}
bool _2sat(int n,int d)
{
int i,j;
Lnum=0;
memset(_next,0,sizeof(_next));
for (i=0;i<n;i++)
for (j=i+1;j<n;j++)
{
if (arc[i<<1][j<<1]<d)
addline(i<<1,j<<1|1),addline(j<<1,i<<1|1);
if (arc[i<<1][j<<1|1]<d)
addline(i<<1,j<<1),addline(j<<1|1,i<<1|1);
if (arc[i<<1|1][j<<1]<d)
addline(i<<1|1,j<<1|1),addline(j<<1,i<<1);
if (arc[i<<1|1][j<<1|1]<d)
addline(i<<1|1,j<<1),addline(j<<1|1,i<<1);
}
memset(dfn,0,sizeof(dfn));
memset(instack,false,sizeof(instack));
while (!mystack.empty()) mystack.pop();
tpnum=DfsIndex=0;
for (i=0;i<(n<<1);i++)
if (!dfn[i]) tarjan(i);
for (i=0;i<n;i++)
if (tp[i<<1]==tp[i<<1|1]) return false;
return true;
}
int main()
{
int n,i;
while (~scanf("%d",&n))
{
for (i=0;i<n;i++) scanf("%d%d%d%d",&b[i].x0,&b[i].y0,&b[i].x1,&b[i].y1);
for (i=0;i<n;i++)
for (int j=i+1;j<n;j++)
{
arc[i<<1][j<<1]=arc[j<<1][i<<1]=dis(b[i].x0,b[i].y0,b[j].x0,b[j].y0);
arc[i<<1][j<<1|1]=arc[j<<1|1][i<<1]=dis(b[i].x0,b[i].y0,b[j].x1,b[j].y1);
arc[i<<1|1][j<<1]=arc[j<<1][i<<1|1]=dis(b[i].x1,b[i].y1,b[j].x0,b[j].y0);
arc[i<<1|1][j<<1|1]=arc[j<<1|1][i<<1|1]=dis(b[i].x1,b[i].y1,b[j].x1,b[j].y1);
}
int l,r,mid;
l=0,r=2*oo;
while (r-l>1)
{
mid=(r+l)/2;
if (_2sat(n,mid)) l=mid;
else r=mid;
}
printf("%.2lf
",sqrt(l)*0.5);
}
return 0;
}
Program-----vector存图..其他同上
#include<iostream>
#include<stdio.h>
#include<string.h>
#include<cmath>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<algorithm>
#define ll long long
#define oo 1000000007
#define pi acos(-1.0)
#define MAXN 205
using namespace std;
struct node
{
int x0,y0,x1,y1;
}b[MAXN];
vector<int> T[MAXN];
int dfn[MAXN],low[MAXN],tp[MAXN],tpnum,DfsIndex,arc[MAXN][MAXN];
bool instack[MAXN];
stack<int> mystack;
int dis(int x0,int y0,int x1,int y1)
{
return (x0-x1)*(x0-x1)+(y0-y1)*(y0-y1);
}
void tarjan(int x)
{
int i,y,m=T[x].size();
dfn[x]=low[x]=++DfsIndex;
instack[x]=true;
mystack.push(x);
for (i=0;i<m;i++)
{
y=T[x][i];
if (!dfn[y])
{
tarjan(y);
low[x]=min(low[x],low[y]);
}else
if (instack[y]) low[x]=min(low[x],dfn[y]);
}
if (dfn[x]==low[x])
{
tpnum++;
do
{
x=mystack.top();
mystack.pop();
instack[x]=false;
tp[x]=tpnum;
}while (dfn[x]!=low[x]);
}
return;
}
bool _2sat(int n,int d)
{
int i,j;
for (i=0;i<(n<<1);i++) T[i].clear(); //小错误..搞了N久才发现..
for (i=0;i<n;i++)
for (j=i+1;j<n;j++)
{
if (arc[i<<1][j<<1]<d)
T[i<<1].push_back(j<<1|1),T[j<<1].push_back(i<<1|1);
if (arc[i<<1][j<<1|1]<d)
T[i<<1].push_back(j<<1),T[(j<<1)|1].push_back(i<<1|1);
if (arc[i<<1|1][j<<1]<d)
T[(i<<1)|1].push_back((j<<1)|1),T[j<<1].push_back(i<<1);
if (arc[i<<1|1][j<<1|1]<d)
T[(i<<1)|1].push_back(j<<1),T[(j<<1)|1].push_back(i<<1);
}
memset(dfn,0,sizeof(dfn));
memset(instack,false,sizeof(instack));
while (!mystack.empty()) mystack.pop();
tpnum=DfsIndex=0;
for (i=0;i<(n<<1);i++)
if (!dfn[i]) tarjan(i);
for (i=0;i<n;i++)
if (tp[i<<1]==tp[i<<1|1]) return false;
return true;
}
int main()
{
int n,i;
while (~scanf("%d",&n))
{
for (i=0;i<n;i++) scanf("%d%d%d%d",&b[i].x0,&b[i].y0,&b[i].x1,&b[i].y1);
for (i=0;i<n;i++)
for (int j=i+1;j<n;j++)
{
arc[i<<1][j<<1]=arc[j<<1][i<<1]=dis(b[i].x0,b[i].y0,b[j].x0,b[j].y0);
arc[i<<1][j<<1|1]=arc[j<<1|1][i<<1]=dis(b[i].x0,b[i].y0,b[j].x1,b[j].y1);
arc[i<<1|1][j<<1]=arc[j<<1][i<<1|1]=dis(b[i].x1,b[i].y1,b[j].x0,b[j].y0);
arc[i<<1|1][j<<1|1]=arc[j<<1|1][i<<1|1]=dis(b[i].x1,b[i].y1,b[j].x1,b[j].y1);
}
int l,r,mid;
l=0,r=2*oo;
while (r-l>1)
{
mid=(r+l)>>1;
if (_2sat(n,mid)) l=mid;
else r=mid;
}
printf("%.2f
",sqrt(l)*0.5);
}
return 0;
}
Program-----vector存图..直接浮点进行运算...
#include<iostream>
#include<stdio.h>
#include<string.h>
#include<cmath>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<algorithm>
#define ll long long
#define eps 1e-5
#define oo 1000000007
#define pi acos(-1.0)
#define MAXN 205
using namespace std;
struct node
{
int x0,y0,x1,y1;
}b[MAXN];
vector<int> T[MAXN];
int dfn[MAXN],low[MAXN],tp[MAXN],tpnum,DfsIndex;
double arc[MAXN][MAXN];
bool instack[MAXN];
stack<int> mystack;
double dis(int x0,int y0,int x1,int y1)
{
return sqrt((x0-x1)*(x0-x1)+(y0-y1)*(y0-y1));
}
void tarjan(int x)
{
int i,y,m=T[x].size();
dfn[x]=low[x]=++DfsIndex;
instack[x]=true;
mystack.push(x);
for (i=0;i<m;i++)
{
y=T[x][i];
if (!dfn[y])
{
tarjan(y);
low[x]=min(low[x],low[y]);
}else
if (instack[y]) low[x]=min(low[x],dfn[y]);
}
if (dfn[x]==low[x])
{
tpnum++;
do
{
x=mystack.top();
mystack.pop();
instack[x]=false;
tp[x]=tpnum;
}while (dfn[x]!=low[x]);
}
return;
}
bool _2sat(int n,double d)
{
int i,j;
for (i=0;i<(n<<1);i++) T[i].clear();
for (i=0;i<n;i++)
for (j=i+1;j<n;j++)
{
if (arc[i<<1][j<<1]+eps<d)
T[i<<1].push_back(j<<1|1),T[j<<1].push_back(i<<1|1);
if (arc[i<<1][j<<1|1]+eps<d)
T[i<<1].push_back(j<<1),T[(j<<1)|1].push_back(i<<1|1);
if (arc[i<<1|1][j<<1]+eps<d)
T[(i<<1)|1].push_back((j<<1)|1),T[j<<1].push_back(i<<1);
if (arc[i<<1|1][j<<1|1]+eps<d)
T[(i<<1)|1].push_back(j<<1),T[(j<<1)|1].push_back(i<<1);
}
memset(dfn,0,sizeof(dfn));
memset(instack,false,sizeof(instack));
while (!mystack.empty()) mystack.pop();
tpnum=DfsIndex=0;
for (i=0;i<(n<<1);i++)
if (!dfn[i]) tarjan(i);
for (i=0;i<n;i++)
if (tp[i<<1]==tp[i<<1|1]) return false;
return true;
}
int main()
{
int n,i;
while (~scanf("%d",&n))
{
for (i=0;i<n;i++) scanf("%d%d%d%d",&b[i].x0,&b[i].y0,&b[i].x1,&b[i].y1);
for (i=0;i<n;i++)
for (int j=i+1;j<n;j++)
{
arc[i<<1][j<<1]=arc[j<<1][i<<1]=dis(b[i].x0,b[i].y0,b[j].x0,b[j].y0);
arc[i<<1][j<<1|1]=arc[j<<1|1][i<<1]=dis(b[i].x0,b[i].y0,b[j].x1,b[j].y1);
arc[i<<1|1][j<<1]=arc[j<<1][i<<1|1]=dis(b[i].x1,b[i].y1,b[j].x0,b[j].y0);
arc[i<<1|1][j<<1|1]=arc[j<<1|1][i<<1|1]=dis(b[i].x1,b[i].y1,b[j].x1,b[j].y1);
}
double l,r,mid;
l=0,r=2*oo;
while (r-l>eps)
{
mid=(r+l)/2;
if (_2sat(n,mid)) l=mid;
else r=mid;
}
printf("%.2lf
",l*0.5);
}
return 0;
}