zoj 3460 Missile【经典建图&&二分】
You control N missile launching towers. Every tower has enough missiles, but for each tower only one missile can be launch at the same time. Before the launching, every missile need T1 seconds to leave the tower. Assume that all the missiles have the same speed V, and it would fly along the shortest path to the target. You can just consider the horizontal distance and ignore the height. You can consider the time equal to distance / V (minutes). The missile can immediately destroy the target when it reached. Besides, for the same tower, after launching a missile, it need T2 minutes to prepare for the next one.
Now, give you the coordinate position of N missile launching towers and M targets, T1, T2 and V, you should find the minimum minutes to destroy all the targets.
Input
The input will consist of about 10 cases. The first line of each case contains five positive integer numbers N, M, T1, T2 and V, decribed as above. The next M lines contains two integer numbers indicating the coordinate of M targets. The continueing N lines contains two integer numbers indicating the coordinate of N towers.
To all the
cases, 1 ≤ N ≤ 50, 1 ≤ M ≤ 50
The absolute value of all the
coordinates will not exceed 10000, T1,
T2, V will not exceed 2000.
Output
For each case, the output is only one line containing only one real number with six digits precision (after a decimal point) indicating the minimum minutes to destroy all the targets.
Sample Input
3 3 30 20 1 0 0 0 50 50 0 50 50 0 1000 1000 0
Sample Output
91.500000
题意：用N个导弹发射塔攻击M个目标。每个导弹发射塔只能同时为一颗导弹服务，发射一颗导弹后需要T1（这里用的是秒）的时间才能离开当前的导弹发射塔，一颗导弹从发射到击中目标的时间与目标到发射塔的距离有关（直线距离），每颗导弹发射完成之后发射塔需要T2的时间准备下一个。现在给出N个导弹发射塔和M个目标的位置坐标以及T1，T2，V，问用这N个导弹发射塔最少需要多少时间可以击毁所有M个目标。
具体实现
一：对每一个导弹发射器，它击中一个目标共有M种情况：分别为在该发射塔第一次发射、第二次发射、第三次发射...一直到第M次发射。因此我们可以把每一个导弹发射塔拆分成M个发射塔，它们与同一个目标的距离是一样的，唯一不同是T1、T2的花销占时不一样。
二：这样的话我们就得到了N*M个点发射器到 M个目标的映射，所表示的关系是当前发射塔击中目标的耗时。
三：设立超级源点0，超级汇点 N * M + M + 1。
四：超级源点到每个发射塔（拆分后的）引一条容量为1的边，每个目标到超级汇点引一条容量为1的边，按若小于当前查询时间的关系（同匹配建边）建边容量为1。
然后跑最大流，判断最大流是否为M。 接着二分查找。
以上解析来自会长大大：http://blog.csdn.net/hpuhjh/article/details/47334625
太弱了 这道题自己建不出来图，
//#include<stdio.h>
//#include<string.h>
//#include<math.h>
//#include<queue>
//#include<stack>
//#include<algorithm>
//#define MAX 110
//#define DD double
//#define INF 0x7fffff
//#define MAXM 500100
//using namespace std;
//struct node
//{
// int from,to,cap,flow,next;
//}edge[MAXM];
//int dis[MAX],vis[MAX];
//int cur[MAX];
//int ans,head[MAX];
//int n,m;
//DD t1,t2,v;
////DD toalx[MAX],toaly[MAX],towrx[MAX],towry[MAX];
//struct record
//{
// DD x,y;
//};
//DD time[3000][MAX];
//DD map[MAX][MAX];
//void init()
//{
// ans=0;
// memset(head,-1,sizeof(head));
//}
//void add(int u,int v,int w)
//{
// edge[ans]={u,v,w,0,head[u]};
// head[u]=ans++;
// edge[ans]={v,u,0,0,head[v]};
// head[v]=ans++;
//}
//DD dist(record a,record b)
//{
// return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
//}
//record towr[MAX];
//record toal[MAX];
//void input()
//{
// int i,j,k;
//
// for(i=1;i<=m;i++)
// scanf("%lf%lf",&toal[i].x,&toal[i].y);
// for(i=1;i<=n;i++)
// scanf("%lf%lf",&towr[i].x,&towr[i].y);
// for(i=1;i<=n;i++)
// for(j=1;j<=m;j++)
// map[i][j]=dist(towr[i],toal[j]);
// for(i=1;i<=n;i++)
// for(k=1;k<=m;k++)
// for(j=1;j<=m;j++)
// time[(i - 1) * m + k][j] = t1 * k + t2 * (k - 1) + map[i][j] / v;
//}
//void getmap(double Max)
//{
// int i,j;
// for(i=1;i<=n*m;i++)
// add(0,i,1);
// for(i=n*m+1;i<=n*m+m;i++)
// add(i,n*m+m+1,1);
// for(i=1;i<=n*m;i++)
// {
// for(j=1;j<=m;j++)
// {
// if(time[i][j]<=Max)
// add(i,j+n*m,1);
// }
// }
//}
//
//
//int bfs(int beg,int end)
//{
// queue<int>q;
// memset(vis,0,sizeof(vis));
// memset(dis,-1,sizeof(dis));
// while(!q.empty()) q.pop();
// vis[beg]=1;
// dis[beg]=0;
// q.push(beg);
// while(!q.empty())
// {
// int u=q.front();
// q.pop();
// for(int i=head[u];i!=-1;i=edge[i].next)
// {
// node E=edge[i];
// if(!vis[E.to]&&E.cap>E.flow)
// {
// dis[E.to]=dis[u]+1;
// vis[E.to]=1;
// if(E.to==end) return 1;
// q.push(E.to);
// }
// }
// }
// return 0;
//}
//int dfs(int x,int a,int end)
//{
// if(x==end||a==0)
// return a;
// int flow=0,f;
// for(int& i=cur[x];i!=-1;i=edge[i].next)
// {
// node& E=edge[i];
// if(dis[E.to]==dis[x]+1&&(f=dfs(E.to,min(a,E.cap-E.flow),end))>0)
// {
// E.flow+=f;
// edge[i^1].flow-=f;
// flow+=f;
// a-=f;
// if(a==0) break;
// }
// }
// return flow;
//}
//int maxflow(int beg,int end)
//{
// int flow=0;
// while(bfs(beg,end))
// {
// memcpy(cur,head,sizeof(head));
// flow+=dfs(beg,INF,end);
// }
// return flow;
//}
//int main()
//{
// int t;
// while(scanf("%d%d%lf%lf%lf",&n,&m,&t1,&t2,&v)!=EOF)
// {
// t1=t1/60;
// input();
// double l=0.0, r =200000000000.0,mid;
// while(r-l>=1e-8)
// {
// mid=(l+r)/2;
// init();
// getmap(mid);
// if(maxflow(0,n*m+m+1)>=m)
// r=mid;
// else
// l=mid;
// }
// printf("%.6lf\n",r);
// }
// return 0;
//}
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <cmath>
#define INF 0x3f3f3f3f
#define maxn 5000
#define maxm 500000
using namespace std;
int head[maxn], cur[maxn], cnt;
int dist[maxn], vis[maxn];
struct node
{
int u,v,cap,flow,next;
};
struct NODE
{
double x, y;
};
node edge[maxm];
NODE tower[60];
NODE target[60];
int N, M;
double T1, T2, V;
double map[60][60];
double Time[3000][60];
double change(NODE a, NODE b)
{
return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}
void init()
{
cnt = 0;
memset(head, -1, sizeof(head));
}
void add(int u, int v, int w){
node E1 = {u, v, w, 0, head[u]};
edge[cnt] = E1;
head[u] = cnt++;
node E2 = {v, u, 0, 0, head[v]};
edge[cnt] = E2;
head[v] = cnt++;
}
void getmap(double max_min)
{
int i, j;
for(i = 1; i <= N * M; ++i)
add(0, i, 1);
for(i = N * M + 1; i <= N * M + M; ++i)
add(i, N * M + M + 1, 1);
for(i = 1; i <= N * M; ++i)
for(j = 1; j <= M; ++j)
if(Time[i][j] <= max_min)//找最小时间建图
add(i, j + N * M, 1);
}
bool BFS(int st, int ed)
{
queue<int>q;
memset(vis, 0, sizeof(vis));
memset(dist, -1, sizeof(dist));
q.push(st);
vis[st] = 1;
dist[st] = 0;
while(!q.empty()){
int u = q.front();
q.pop();
for(int i = head[u]; i != -1; i = edge[i].next){
node E = edge[i];
if(!vis[E.v] && E.cap > E.flow){
vis[E.v] = 1;
dist[E.v] = dist[u] + 1;
if(E.v == ed) return true;
q.push(E.v);
}
}
}
return false;
}
int DFS(int x, int ed, int a)
{
if(a == 0 || x == ed)
return a;
int flow = 0, f;
for(int &i = cur[x]; i != -1; i =edge[i].next)
{
node &E = edge[i];
if(dist[E.v] == dist[x] + 1 && (f = DFS(E.v, ed, min(a, E.cap - E.flow))) > 0){
E.flow += f;
edge[i ^ 1].flow -= f;
flow += f;
a -= f;
if(a == 0) break;
}
}
return flow;
}
int maxflow (int st, int ed)
{
int flowsum = 0;
while(BFS(st, ed))
{
memcpy(cur, head, sizeof(head));
flowsum += DFS(st, ed, INF);
}
return flowsum;
}
int main ()
{
while(scanf("%d%d%lf%lf%lf", &N, &M, &T1, &T2, &V) != EOF){
T1 = T1 / 60;//t1给的单位是秒 要转换为分
int i, j, k;
for(j = 1; j <= M; ++j)
scanf("%lf%lf", &target[j].x, &target[j].y);
for(i = 1; i <= N; ++i)
scanf("%lf%lf", &tower[i].x, &tower[i].y);
for(i = 1; i <= N; ++i)
for(j = 1; j <= M; ++j)
map[i][j] = change(tower[i], target[j]);
//map[][]表示第i个塔到j个目标的距离
for(i = 1; i <= N; ++i)
for(k = 1; k <= M; ++k)//k表示的是发射第k个导弹
{
for(j = 1; j <= M; ++j)
Time[(i - 1) * M + k][j] = T1 * k + T2 * (k - 1) + map[i][j] / V;
//Time[][]数组表示从第i个塔依次发射炮弹到每个目标所分别需要的时间
}
double l = 0.0, r = 200000000000.0, mid;
while(r - l >= 1e-8)
{
mid = (l + r) / 2;
init();
getmap(mid);//每次补充建图
if(maxflow(0, N * M + M + 1) >= M)
r = mid;
else
l = mid;
}
printf("%.6lf\n", r);
}
return 0;
}
