思路：
并查集。
实现：
1 #include <iostream> 2 #include <cstdio> 3 #include <cmath> 4 using namespace std; 5 6 struct node 7 { 8 int x, y; 9 }; 10 node a[1005]; 11 char t; 12 int n, p, q; 13 double d; 14 int ran[1005]; 15 int par[1005]; 16 bool ok[1005]; 17 18 double dis[1005][1005]; 19 20 double square(int a) 21 { 22 return a * a; 23 } 24 25 void init() 26 { 27 for (int i = 1; i <= n; i++) 28 { 29 for (int j = 1; j <= n; j++) 30 { 31 dis[i][j] = sqrt(square(a[i].x - a[j].x) + square(a[i].y - a[j].y)); 32 } 33 par[i] = i; 34 ran[i] = 0; 35 } 36 } 37 38 int find(int x) 39 { 40 if (par[x] == x) 41 return x; 42 return par[x] = find(par[x]); 43 } 44 45 void unite(int x, int y) 46 { 47 x = find(x); 48 y = find(y); 49 if (x == y) 50 return; 51 if (ran[x] < ran[y]) 52 { 53 par[x] = y; 54 } 55 else 56 { 57 par[y] = x; 58 if (ran[x] == ran[y]) 59 { 60 ran[x]++; 61 } 62 } 63 } 64 65 bool same(int x, int y) 66 { 67 return find(x) == find(y); 68 } 69 70 int main() 71 { 72 scanf("%d %lf", &n, &d); 73 for (int i = 1; i <= n; i++) 74 { 75 scanf("%d %d", &a[i].x, &a[i].y); 76 } 77 getchar(); 78 init(); 79 while (scanf("%c", &t) != EOF) 80 { 81 if (t == 'O') 82 { 83 scanf("%d", &p); 84 getchar(); 85 for (int j = 1; j <= n; j++) 86 { 87 if (dis[p][j] <= d && ok[j]) 88 { 89 unite(p, j); 90 } 91 } 92 ok[p] = true; 93 } 94 else 95 { 96 scanf("%d %d", &p, &q); 97 getchar(); 98 if (same(p, q)) 99 puts("SUCCESS"); 100 else 101 puts("FAIL"); 102 } 103 } 104 return 0; 105 }