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 }

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