loj 1154(最大流+枚举汇点)

题目链接：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=26868
思路：拆点，容量为最多能跳的步数，然后设立一个超级源点，源点与各点两连边，容量为一开始的企鹅数，最后就是枚举汇点了，跑最大流验证即可。
  1 #include<iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<algorithm>
  5 #include<queue>
  6 #include<cmath>
  7 using namespace std;
  8 #define MAXN 222
  9 #define MAXM 222222
 10 #define inf 1<<30
 11 #define FILL(a,b) memset(a,b,sizeof(a))
 12 
 13 struct Edge{
 14     int v,cap,next;
 15 }edge[MAXM];
 16 
 17 int n,vs,vt,NV,NE,head[MAXN];
 18 double d;
 19 
 20 
 21 void Insert(int u,int v,int cap)
 22 {
 23     edge[NE].v=v;
 24     edge[NE].cap=cap;
 25     edge[NE].next=head[u];
 26     head[u]=NE++;
 27 
 28     edge[NE].v=u;
 29     edge[NE].cap=0;
 30     edge[NE].next=head[v];
 31     head[v]=NE++;
 32 }
 33 
 34 int level[MAXN],gap[MAXN];
 35 void bfs(int vt)
 36 {
 37     FILL(level,-1);
 38     FILL(gap,0);
 39     queue<int>que;
 40     que.push(vt);
 41     level[vt]=0;
 42     gap[0]++;
 43     while(!que.empty()){
 44         int u=que.front();
 45         que.pop();
 46         for(int i=head[u];i!=-1;i=edge[i].next){
 47             int v=edge[i].v;
 48             if(level[v]!=-1)continue;
 49             level[v]=level[u]+1;
 50             gap[level[v]]++;
 51             que.push(v);
 52         }
 53     }
 54 }
 55 
 56 int pre[MAXN],cur[MAXN];
 57 int SAP(int vs,int vt)
 58 {
 59     bfs(vt);
 60     memcpy(cur,head,sizeof(head));
 61     int u=pre[vs]=vs,aug=inf,maxflow=0;
 62     gap[0]=NV;
 63     while(level[vs]<NV){
 64         bool flag=false;
 65         for(int &i=cur[u];i!=-1;i=edge[i].next){
 66             int v=edge[i].v;
 67             if(edge[i].cap>0&&level[u]==level[v]+1){
 68                 flag=true;
 69                 aug=min(aug,edge[i].cap);
 70                 pre[v]=u;
 71                 u=v;
 72                 if(v==vt){
 73                     maxflow+=aug;
 74                     for(u=pre[u];v!=vs;v=u,u=pre[u]){
 75                         edge[cur[u]].cap-=aug;
 76                         edge[cur[u]^1].cap+=aug;
 77                     }
 78                     aug=inf;
 79                 }
 80                 break;
 81             }
 82         }
 83         if(flag)continue;
 84         int minlevel=NV;
 85         for(int i=head[u];i!=-1;i=edge[i].next){
 86             int v=edge[i].v;
 87             if(edge[i].cap>0&&level[v]<minlevel){
 88                 cur[u]=i;
 89                 minlevel=level[v];
 90             }
 91         }
 92         if(--gap[level[u]]==0)break;
 93         level[u]=minlevel+1;
 94         gap[level[u]]++;
 95         u=pre[u];
 96     }
 97     return maxflow;
 98 }
 99 
100 struct Node{
101     double x,y;
102     int num,step;
103 }node[MAXN];
104 
105 double Get_Dist(int i,int j)
106 {
107     double d1=(node[i].x-node[j].x)*(node[i].x-node[j].x);
108     double d2=(node[i].y-node[j].y)*(node[i].y-node[j].y);
109     return sqrt(d1+d2);
110 }
111 
112 void Build(int ed)
113 {
114     NE=0;
115     FILL(head,-1);
116     vs=0,vt=2*n+1;
117     NV=vt+1;
118     for(int i=1;i<=n;i++){
119         Insert(i,i+n,node[i].step);
120         Insert(vs,i,node[i].num);
121     }
122     for(int i=1;i<=n;i++){
123         for(int j=i+1;j<=n;j++){
124             if(Get_Dist(i,j)<=d){
125                 Insert(i+n,j,inf);
126                 Insert(j+n,i,inf);
127             }
128         }
129     }
130     Insert(ed,vt,inf);
131 }
132 
133 int main()
134 {
135     int _case,ans,sum,flag,t=1;
136     scanf("%d",&_case);
137     while(_case--){
138         scanf("%d%lf",&n,&d);
139         sum=0;
140         for(int i=1;i<=n;i++){
141             scanf("%lf%lf%d%d",&node[i].x,&node[i].y,&node[i].num,&node[i].step);
142             sum+=node[i].num;
143         }
144         flag=0;
145         printf("Case %d:",t++);
146         //枚举集中点
147         for(int i=1;i<=n;i++){
148             Build(i);
149             if(SAP(vs,vt)==sum)flag=1,printf(" %d",i-1);
150         }
151         if(!flag)printf(" -1");
152         puts("");
153     }
154     return 0;
155 }
View Code