http://acm.hdu.edu.cn/showproblem.php?pid=2389
题意：给暴风雨到来的时刻，m个人的坐标和单位速度，和n个救生衣的坐标。每个救生衣只能匹配一个人，求最多有多少人可以得到救生衣。
题解：典型二分图最大匹配题型。因为点比较多，使用Hopcroft-Karp算法。讲解：http://blog.csdn.net/wall_f/article/details/8248373
http://www.cnblogs.com/-sunshine/archive/2012/08/30/2664242.html
1 #include <iostream> 2 #include <cstring> 3 #include <cstdio> 4 #include <cstdlib> 5 #include <cmath> 6 #include <string> 7 #include <vector> 8 #include <list> 9 #include <map> 10 #include <queue> 11 #include <stack> 12 #include <bitset> 13 #include <algorithm> 14 #include <numeric> 15 #include <functional> 16 #include <set> 17 #include <fstream> 18 19 using namespace std; 20 const int maxn=3010; 21 const int INF=1<<28; 22 bool used[maxn]; 23 struct guest{ 24 int x; 25 int y; 26 int speed; 27 }gu[maxn]; 28 struct umbrellas{ 29 int x; 30 int y; 31 }um[maxn]; 32 int mymap[maxn][maxn]; 33 int dis; 34 int cx[maxn],cy[maxn],dx[maxn],dy[maxn]; 35 int V; 36 int ca,t,m,n; 37 38 bool searchpath() 39 { 40 queue<int> Q; 41 dis=INF; 42 memset(dx, -1, sizeof(dx)); 43 memset(dy, -1, sizeof(dy)); 44 for (int i=0; i<V; i++) { 45 if (cx[i]==-1) { 46 Q.push(i); 47 dx[i]=0; 48 } 49 } 50 while (!Q.empty()) { 51 int u=Q.front(); 52 Q.pop(); 53 if (dx[u]>dis) { 54 break; 55 } 56 for (int v=0; v<V; v++) { 57 if (mymap[u][v]&&dy[v]==-1) { 58 dy[v]=dx[u]+1; 59 if (cy[v]==-1) { 60 dis=dy[v]; 61 } 62 else { 63 dx[cy[v]]=dy[v]+1; 64 Q.push(cy[v]); 65 } 66 } 67 } 68 } 69 return dis!=INF; 70 } 71 72 int findpath(int u) 73 { 74 for (int v=0; v<n; v++) { 75 if (!used[v]&&mymap[u][v]&&dy[v]==dx[u]+1) { 76 used[v]=1; 77 if (cy[v]!=-1&&dy[v]==dis) { 78 continue; 79 } 80 if (cy[v]==-1||findpath(cy[v])) { 81 cy[v]=u; 82 cx[u]=v; 83 return 1; 84 } 85 } 86 } 87 return 0; 88 } 89 90 void binary_match() 91 { 92 int res=0; 93 memset(cx, -1, sizeof(cx)); 94 memset(cy, -1, sizeof(cy)); 95 while (searchpath()) { 96 memset(used,0,sizeof(used)); 97 for (int i=0; i<V; i++) { 98 if (cx[i]==-1) { 99 res+=findpath(i); 100 } 101 } 102 } 103 printf("%d ",res); 104 } 105 int main() 106 { 107 //freopen("/Users/apple/Desktop/hdu 2389/hdu 2389/in", "r", stdin); 108 //freopen("/Users/apple/Desktop/hdu 2389/hdu 2389/out", "w", stdout); 109 110 scanf("%d",&ca); 111 for (int num=1; num<=ca; num++) { 112 scanf("%d",&t); 113 scanf("%d",&m); 114 for (int i=0; i<m; i++) { 115 scanf("%d%d%d",&gu[i].x,&gu[i].y,&gu[i].speed); 116 } 117 scanf("%d",&n); 118 for (int i=0; i<n; i++) { 119 scanf("%d%d",&um[i].x,&um[i].y); 120 } 121 memset(mymap, 0, sizeof(mymap)); 122 V=m; 123 for (int i=0; i<m; i++) { 124 for (int j=0; j<n; j++) { 125 if (pow(gu[i].x-um[j].x,2)+pow(gu[i].y-um[j].y,2)<=t*t*gu[i].speed*gu[i].speed) { 126 mymap[i][j]=1; 127 } 128 } 129 } 130 printf("Scenario #%d: ",num); 131 binary_match(); 132 puts(""); 133 } 134 return 0; 135 }