poj3565 Ants

使用KM算法，我写过一个，思路是把蚂蚁和树分为两个集合，但是莫名其妙的错了，然后在网上又查了一段代码，和我的方法相同，甚至代码内容差不多，但人家A了，郁闷啊。。。求助。

错误代码：

#include<iostream>#include<cmath>using namespace std;const int MAXN = 101;const int inf = 0x3ffffff;double edge[MAXN][MAXN];bool vis_x[MAXN],vis_y[MAXN];double lx[MAXN],ly[MAXN];int result[MAXN];struct points{double x;double y;}vetex[2*MAXN];bool find(int a,int n){vis_x[a] = true;for(int i=1;i!=n+1;i++){if(!vis_y[i]&&edge[a][i] == lx[a] + ly[i]){vis_y[i] = true;if(result[i]==-1||find(result[i],n)){result[i] = a;return true;}}}return false;}void KM(int n){for(int i=1;i!=n+1;i++){lx[i] = -inf;ly[i] = 0;for(int j=1;j!=n+1;j++)if (lx [i] < edge [i] [j])lx [i] = edge [i] [j];}memset(result,-1,sizeof(result));for(int u = 1;u!=n+1;u++){while(1){memset(vis_x,0,sizeof(vis_x));memset(vis_y,0,sizeof(vis_y));if(find(u,n))break;double dx = inf;for (int i = 1; i<=n+1;i++)if (vis_x [i])for (int j = 1; j<=n+1;j++)if(!vis_y [j])dx = min (lx[i]+ly[j]-edge[i][j],dx);for (int i = 1;i <= n+1;i++){if (vis_x[i])lx[i] -= dx;if (vis_y[i])ly[i] += dx;}}}for(int i=1;i!=n+1;i++){cout<<result[i]<<endl;}}int main(){int T;while(cin>>T){memset(edge,0,sizeof(edge));for(int k=1;k!=2*T+1;k++)cin>>vetex[k].x>>vetex[k].y;for(int k=1;k!=T+1;k++){for(int j=T+1;j!=2*T+1;j++){double num1 = (vetex[k].x-vetex[j].x)*(vetex[k].x-vetex[j].x);double num2 = (vetex[k].y-vetex[j].y)*(vetex[k].y-vetex[j].y);num1+=num2;edge[k][j-T] = -sqrt(num1);}}KM(T);}return 0;}

正确代码：

#include<stdio.h>#include<math.h>#include<string.h>#include<algorithm>#define inf 99999999.0using namespace std;struct Point{double x;double y;};Point ant[105];Point tree[105];double map[105][105];int link[105];double lx[105];double ly[105];bool x[105];bool y[105];int n;double dist(Point a,Point b){return -sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}void init(){int i,j;for(i=0;i<105;i++){lx[i]=inf;ly[i]=0;link[i]=-1;}for(i=0;i<105;i++)for(j=0;j<105;j++)map[i][j]=0;}bool judge(int v,int i){double esp;esp=0.0001;double r=lx[v]+ly[i];double z=map[v][i];if(abs(r-z)<=esp)return true;elsereturn false;}bool find(int v){int i;x[v]=true;for(i=1;i<=n;i++){if(!y[i]&&judge(v,i)){y[i]=true;if(link[i]==-1||find(link[i])){link[i]=v;return true;}}}return false;}int main(){int i,j,k;double d;init();scanf("%d",&n);for(i=1;i<=n;i++)scanf("%lf%lf",&ant[i].x,&ant[i].y);for(i=1;i<=n;i++)scanf("%lf%lf",&tree[i].x,&tree[i].y);for(i=1;i<=n;i++){for(j=1;j<=n;j++){map[i][j]=dist(ant[i],tree[j]);//printf("%lf ",map[i][j]);}//printf("/n");}for(k=1;k<=n;k++){while(1){memset(x,0,sizeof(x));memset(y,0,sizeof(y));if(find(k))break;d=inf;for(i=1;i<=n;i++)if(x[i])for(j=1;j<=n;j++)if(!y[j]&&(lx[i]+ly[j]-map[i][j]<d))d=lx[i]+ly[j]-map[i][j];for(i=1;i<=n;i++)if(x[i])lx[i]=lx[i]-d;for(i=1;i<=n;i++)if(y[i])ly[i]=ly[i]+d;}}double uva=0.0;for(i=1;i<=n;i++)for(j=1;j<=n;j++){if(link[j]==i){printf("%d\n",j);break;}}system("pause");return 0;}