Wireless Network POJ - 2236 并查集

一、内容

An earthquake takes place in Southeast Asia. The ACM (Asia Cooperated Medical team) have set up a wireless network with the lap computers, but an unexpected aftershock attacked, all computers in the network were all broken. The computers are repaired one by one, and the network gradually began to work again. Because of the hardware restricts, each computer can only directly communicate with the computers that are not farther than d meters from it. But every computer can be regarded as the intermediary of the communication between two other computers, that is to say computer A and computer B can communicate if computer A and computer B can communicate directly or there is a computer C that can communicate with both A and B.

In the process of repairing the network, workers can take two kinds of operations at every moment, repairing a computer, or testing if two computers can communicate. Your job is to answer all the testing operations.

Input

The first line contains two integers N and d (1 <= N <= 1001, 0 <= d <= 20000). Here N is the number of computers, which are numbered from 1 to N, and D is the maximum distance two computers can communicate directly. In the next N lines, each contains two integers xi, yi (0 <= xi, yi <= 10000), which is the coordinate of N computers. From the (N+1)-th line to the end of input, there are operations, which are carried out one by one. Each line contains an operation in one of following two formats:
1. "O p" (1 <= p <= N), which means repairing computer p.
2. "S p q" (1 <= p, q <= N), which means testing whether computer p and q can communicate.

The input will not exceed 300000 lines.

Output

For each Testing operation, print "SUCCESS" if the two computers can communicate, or "FAIL" if not. 

Sample Input

4 1
0 1
0 2
0 3
0 4
O 1
O 2
O 4
S 1 4
O 3
S 1 4

Sample Output

FAIL
SUCCESS

二、思路

• 并查集
• 用vis记录电脑是否修复，修复了就不再修复。 fix记录修复后的电脑的下标，每当修复一台新的电脑，那么就循环遍历以前修复过的电脑，看是否能连通，如果能连通就合并。
• 最后判断2台电脑是否能连通就可以了。

三、代码

#include 
#include 
#include 
#include 
using namespace std;
const int N = 1005;
struct P {
	int x, y;
} point[N]; 
int n, d, p[N], u, v, cnt, fix[N];
char str[2];
bool vis[N];
int find(int x) {
	return x == p[x] ? x : (p[x] = find(p[x]));
}
double getD(int u, int v) {
	int x = point[u].x - point[v].x;
	int y = point[u].y - point[v].y;
	return sqrt(1.0 * x * x + 1.0 * y * y);
}
int main() {
	scanf("%d%d", &n, &d);
	for (int i = 1; i <= n; i++) p[i] = i;
	for (int i = 1; i <= n; i++) {
		scanf("%d%d", &point[i].x, &point[i].y);
	} 
	while (scanf("%s", str) != EOF) {
		if (str[0] == 'O') {
			scanf("%d", &v); 
			if (vis[v]) continue; //代表已经 修复 
			vis[v] = true;
			fix[++cnt] = v;
			for (int i = 1; i < cnt; i++) {
				//判断新添加的是否连通
				u = fix[i];
				double t = getD(u, v);	 
				if (t <= d) {
					//进行合并
					 int fu = find(u);
					 int fv = find(v);
					 p[fu] = fv;
				}
			}
		} else {
			//判断2个点是否连通
			scanf("%d%d", &u, &v); 
			int fu = find(u);
			int fv = find(v);
			if (fu == fv) printf("SUCCESS\n");
			else printf("FAIL\n");
		}
	 }	
	return 0;
}