HDU 1875(最小生成树)

对的代码：

#include <stdio.h>#include <cstring>#include <cmath>#define INF 0xfffffff #define max 105double map[max][max],lowcost[max],sum;bool visited[max];struct coord{double x,y;}point[max];double distance (coord a,coord b){  //a点与b点之间的距离return sqrt ((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}int Prime (int n){    //普利姆算法int cnt=0;double tmp;memset (visited,0,sizeof (visited));  //所有节点的访问变量 初始化为假visited[1] = true;  //从第一个节点开始访问sum = 0;for (int i=1;i<=n;i++)lowcost[i] = map[1][i];for (int i=1;i<=n;i++){tmp = INF;int k=-1;for (int j=1;j<=n;j++)if (!visited[j] && lowcost[j] < tmp)tmp = lowcost[k=j];if (k==-1 || tmp == INF) break;visited[k] = 1;sum += tmp;cnt++;for (int i=1;i<=n;i++)if (!visited[i] && map[k][i] < lowcost[i])lowcost[i] = map[k][i];}//printf("cnt == %d\n",cnt);return cnt;}int main (){int t;scanf ("%d",&t);while (t--){int n;for (int i=1;i<=max;i++){//所有岛之间距离初始化无穷大。for (int j=i;j<=max;j++)map[i][j] = map[j][i] = INF;}scanf ("%d",&n);for (int i=1;i<=n;i++) //输入n个点的坐标scanf ("%lf%lf",&point[i].x,&point[i].y);for (int i=1;i<n;i++)  //遍历所有可以修路的两个小岛for (int j=i+1;j<=n;j++){double tmp = distance(point[i],point[j]);if (tmp <= 1000 && tmp >= 10)map[i][j] = map[j][i] = tmp;}if (Prime (n) == n-1)  //可以实现全部畅通printf ("%.1lf\n",sum*100);elseputs ("oh!");}return 0;}

WA了n多次的代码：

#include <stdio.h>#include <cstring>#include <cmath>#define INF 0xfffffff #define max 105double map[max][max],lowcost[max],sum;bool visited[max];struct coord{double x,y;}point[max];double distance (coord a,coord b){return sqrt ((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}int Prime (int n){    //普利姆算法int k=0,cnt=0;double tmp;memset (visited,0,sizeof (visited));visited[1] = true;sum = 0;for (int i=1;i<=n;i++)lowcost[i] = map[1][i];for (int i=1;i<=n;i++){tmp = INF;for (int j=1;j<=n;j++)if (!visited[j] && lowcost[j] < tmp)tmp = lowcost[k=j];if (tmp == INF) break;visited[k] = 1;sum += tmp;cnt++;for (int i=1;i<=n;i++)if (!visited[i] && map[k][i] < lowcost[i])lowcost[i] = map[k][i];}return cnt;}int main (){int t;scanf ("%d",&t);while (t--){int n;memset (map,INF,sizeof (map));//所有岛之间距离初始化无穷大。scanf ("%d",&n);for (int i=1;i<=n;i++) //输入n个点的坐标scanf ("%lf%lf",&point[i].x,&point[i].y);for (int i=1;i<n;i++)  //遍历所有可以修路的两个小岛for (int j=i+1;j<=n;j++){double tmp = distance(point[i],point[j]);if (tmp <= 1000 && tmp >= 10)map[i][j] = map[j][i] = tmp;}if (Prime (n) == n-1)  //可以实现全部畅通printf ("%.1lf\n",sum*100);elseputs ("oh!");}return 0;}

对比两个代码其实就是主函数中对map赋值的地方不一样，结果就是完全相反。。我是在也不相信库函数了。

WA了n多次的并查集代码：

#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>using namespace std;#define max 105struct Point{  //  Coorddouble x,y;}point[max];struct Node{int a;int b;double cost;}node[100010];int cmp (const Node &a,const Node &b){return a.cost < b.cost;}double dis (Point a,Point b){   // Distance return sqrt ((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}int bleg[max];int find (int x){int y = x;while (y != x)y = bleg[x];while (x != bleg[x]){int px = bleg[x];bleg[x] = y;x = px;}return y;}bool Union (int a,int b){int pa = find(a),pb= find (b);if (pa==pb) return false;elsebleg[pa] = pb;return true;}void init (int n){for (int i=1;i<=n;i++) bleg[i] = i;}int main (){int t;scanf ("%d",&t);while (t--){int n,cnt=0,k=1;scanf ("%d",&n);init (n);for (int i=1;i<=n;i++)scanf ("%lf%lf",&point[i].x,&point[i].y);for (int i=1;i<n;i++)  //遍历出所有的可以联通的小岛for (int j=i+1;j<=n;j++){double tmp = dis (point[i],point[j]);if (tmp >= 10 && tmp <= 1000){  //两岛之间的距离满足可以修路的条件node[k].a=i;node[k].b=j;node[k++].cost=tmp;}}k--;  //  k从1开始，所有最后要退一位。sort (node+1,node+k+1,cmp);  //按权值进行从下到大的排序//for (int i=1;i<=k;i++)//printf ("%.3lf\n",node[i].cost);//----并查集部分double sum = 0.0;for (int i=1;i<=k;i++){if (cnt==n-1) break;if (Union (node[i].a,node[i].b)){sum += node[i].cost;  //累加权值cnt++;}}//printf ("cnt==%d\n",cnt);if (cnt==n-1) //可以全部联通printf ("%.1lf\n",sum * 100);elseputs ("oh!");}return 0;}