ZOJ 1914 Prim Kruskal

先计算出最小生成树，然后在输出第p-s小的边

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
#define N 501
#define Maxint 9999999

double c

,x
,y
,dist
;
int s
, closest
,n;

int cmp(const void *a,const void *b)
{
return *(double *)a > *(double *)b ? 1 : -1;
}

void Prim(int v)
{
int i,j,k;
double min,lowcost
;
s[v] = 1;
for(i=1; i<n; i++)
{
lowcost[i] = c[v][i];
closest[i] = v;
s[i] = 0;
}
for(i=1; i<n; i++)
{
min = Maxint;
j = 1;
for(k=1; k<n; k++)
{
if((lowcost[k]<min)&&(!s[k]))
{
min = lowcost[k];
j = k;
}
}
s[j] = 1;
lowcost[j] = min;
dist[i-1] = min;//存放最小生成树的值，将每个最小的边都存起来
for(k = 0; k<n; k++)
{
if((c[j][k]<lowcost[k])&&(!s[k]))
{
lowcost[k] = c[j][k];
closest[k] = j;
}
}
}
}

int main()
{
int i,j,m,ncases;

scanf("%d",&ncases);
while( ncases-- )
{
scanf("%d%d",&m,&n);
for(i=0; i<n; i++)
{
scanf("%lf%lf",&x[i],&y[i]);
for(j=0; j<=i; j++)
{
c[i][j] = sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
c[j][i] = c[i][j];
}
}
Prim(0);
qsort(dist,n-1,sizeof(dist[0]),cmp);
printf("%.2lf\n",dist[n-m-1]);
}
return 0;
}

然后我用Kruskal 做了一遍，既然只要输出第 p-s 小的边，那么我可以不用生成树，即用并查集的方式直接找出第p-s小的边然后输出即可，但是WA的好多次，于是我就随机生成数据，然后用上面正确的代码生成正确的数据和 Kruskal 代码出来的结果对比，最后发现_index写在里面出去的值就自动变为0 了，太尼玛。。。。无语了。

#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

#define NLEN 10000
#define ELEN 500000

typedef struct Edge {
int u, v;
double w;
}Edge;
Edge e[ELEN];

typedef struct Point {
int x, y;
}Point;
Point point[NLEN];
int p[NLEN];

void init(int n) {
for(int i = 0; i < n; i++) {
p[i] = i;
}
}

double dis(int i, int j) {
int xx = abs(point[i].x - point[j].x);
int yy = abs(point[i].y - point[j].y);
double ans = sqrt(xx*xx + yy*yy);
return ans;
}

bool cmp(Edge a, Edge b) {
return a.w < b.w;
}

int find(int x) {
return p[x] == x ? x : (p[x] = find(p[x]));
}

double kruskal(int num, int s) {
int m = 0;
for(int i = 0; i < num; i++) {
int t1 = find(e[i].u);
int t2 = find(e[i].v);
if(t1 != t2) {
p[t1] = t2;
m++;
}
if(m == s) {
return e[i].w;
}
}
}

int main() {
int t;
int s, p;
//	FILE* fp = freopen("out_main", "w", stdout);
//	freopen("in", "r", stdin);
scanf("%d", &t);
while(t--) {
int _index = 0;
scanf("%d%d", &s, &p);
for(int i = 0; i < p; i++) {
scanf("%d%d", &point[i].x, &point[i].y);
}
for(int i = 0; i < p; i++) {
for(int j = i+1; j < p; j++) {
e[_index].u = i;
e[_index].v = j;
e[_index++].w = dis(i, j);
}
}
init(p);
sort(e, e+_index, cmp);
//		for(int i = 0; i < _index; i++) {
//			printf("%.2lf ", e[i].w);
//		}
//		printf("\n");
double ans = kruskal(_index, p-s);
printf("%.2lf\n", ans);
//		fprintf(fp, "%.2lf\n", ans);
}
//	fclose(fp);
//	fclose(stdout);
//	fclose(stdin);
return 0;
}

这里顺便贴上随机数生成的代码吧：

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <stdlib.h>

using namespace std;

#define TESTS 10

#define random(x) (rand()%x)

int main() {
FILE *fp;
int t = TESTS;
fp = freopen("in", "w", stdin);
fprintf(fp, "%d\n", t);
for(int i = 0; i < TESTS; i++) {
int p = random(10);
int s = random(p);
fprintf(fp, "%d %d\n", s, p);
for(int j = 0; j < p; j++) {
int x = random(10000);
int y = random(10000);
fprintf(fp, "%d %d\n", x, y);
}
}
return 0;
}