POJ 2253 Frogger (最小生成树.Prim)

从点 1 开始生成最小生成树，直到将点 2 加入到树中，返回树中最大的边即可。

基本算法是Prim。

#include
#include
#include
#define FOR(i, N) for(int i = 1; i <= (N); i++)
using namespace std;

double cost[500][500];
int coordinate[500][2];

void read(int N){
	FOR(i, N){
		int x, y;
		cin >> x >> y;
		FOR(j, i){
			coordinate[i][0] = x;
			coordinate[i][1] = y;
			int x0 = coordinate[j][0];
			int y0 = coordinate[j][1];
			double dist = sqrt(pow(x0 - x, 2.0) + pow(y0 - y, 2.0));
			cost[i][j] = cost[j][i] = dist;
		}
	}
}

double prim(int N){
	bool inTree[500];
	FOR(i, N)
		inTree[i] = false;
	inTree[1] = true;
	double MAX = -1;
	FOR(i, N - 1){
		double minCost = 10000000;
		int index;
		FOR(k, N){
			if(inTree[k]){
				FOR(j, N){
					if(!inTree[j] && minCost > cost[k][j]){
						minCost = cost[k][j];
						index = j;
					}
				}
			}
		}
			MAX = max(MAX, minCost);
		inTree[index] = true;
		//cout << MAX << " " << index << endl;
		if(index == 2)
			break;
	}
	return MAX;
}

int main(){
	int N, caseNo = 0;
	while(cin >> N && N != 0){
		read(N);
		printf("Scenario #%d\nFrog Distance = %.03f\n\n",++caseNo, prim(N));
		
	}
}