C :

#include<stdio.h>
int p[100005];
int find(int i)
{
    if(p[i]!=i) p[i]=find(p[i]);
    return p[i];
}
int main(void)
{
    int n,d;
    while(scanf("%d%d",&n,&d)!=EOF)
    {
        int i,a[10005],b[10005],c,e,j,x1,x2;
        for(i=1;i<=n;i++)
            p[i]=i;
        for(i=1;i<=n;i++)
            scanf("%d%d",&a[i],&b[i]);
        for(i=1;i<=n;i++)
            for(j=1;j<i;j++)
            if((a[i]-a[j])*(a[i]-a[j])+(b[i]-b[j])*(b[i]-b[j])<=d*d)
            {
                x1=find(i);x2=find(j);

                if(x1!=x2) p[x1]=x2;
            }
        scanf("%d%d",&c,&e);
        if(find(c)==find(e)) printf("SUCCESS\n");
        else printf("FAIL\n");
    }
    return 0;
}

C++ :

//4340K	3079MS
#include<stdio.h>
#include<string.h>
#include<math.h>
#define M 1007
char s[5];
int x[M],y[M],pre[M],vis[M],g[M][M];
int n,d;
void init()
{
    memset(g,0,sizeof(g));
    for(int i=1; i<=n; i++)
    {
        pre[i]=i;
        vis[i]=0;
    }

}
int find(int x)
{
    while(x!=pre[x])
        x=pre[x];
    return x;
}
void unio(int a,int b)
{
    int c=find(a);
    int d=find(b);
    pre[c]=d;
}
bool judge(int i,int j)
{
    return ((y[j]-y[i])*(y[j]-y[i])+(x[j]-x[i])*(x[j]-x[i]))<=d*d;
}
int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    while(scanf("%d%d",&n,&d)!=EOF)
    {
        init();
        int a,b,c;
        for(int i=1; i<=n; i++)
            scanf("%d%d",&x[i],&y[i]);
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
                if(i!=j&&judge(i,j))
                    unio(i,j);
        scanf("%d%d",&a,&b);
        if(find(a)==find(b))printf("SUCCESS\n");
        else printf("FAIL\n");
    }
    return 0;
}