uva10397

已经存在一些边，求其最小生成树。

可以把存在的边权赋值为0，那么做最小生成树的时候一定会把存在的边给选进去，然后最裸的最小生成树即可。

hdu1879也可以这样。

AC代码：

#include <cstdio>#include <string.h>#include <cmath>#define max(a,b) ((a) > (b)) ? (a) : (b)const int MAX_POINT = 770;const int INF = 10000000;const double eps = 1e-6;struct Point {int x;int y;};struct Point point[MAX_POINT];double maps[MAX_POINT][MAX_POINT];double lowest[MAX_POINT], ans;int vis[MAX_POINT];int point_number, exist_number;double getDistance(int i, int j) {int x = point[i].x - point[j].x;int y = point[i].y - point[j].y;return sqrt(x * x + y * y + eps);}void prim() {memset(vis, 0, sizeof(vis));memset(lowest, 0, sizeof(lowest));for (int i = 1; i <= point_number; i++) {lowest[i] = maps[1][i];}vis[1] = 1;ans = 0;for (int i = 1; i < point_number; i++) {double min_ans = INF;int cnt_point;for (int j = 1; j <= point_number; j++) {if (!vis[j] && lowest[j] < min_ans) {cnt_point = j;min_ans = lowest[j];}}ans += min_ans;vis[cnt_point] = 1;for (int j = 1; j <= point_number; j++) {if (!vis[j] && lowest[j] > maps[cnt_point][j]) {lowest[j] = maps[cnt_point][j];}}}}int main() {while (scanf("%d", &point_number) != EOF) {memset(maps, 0, sizeof(maps));for (int i = 1; i <= point_number; i++) {scanf("%d%d", &point[i].x, &point[i].y);}for (int i = 1; i <= point_number; i++) {maps[i][i] = 0;for (int j = i + 1; j <= point_number; j++) {maps[i][j] = maps[j][i] = getDistance(i, j);}}scanf("%d", &exist_number);for (int i = 1; i <= exist_number; i++) {int start, end;scanf("%d%d", &start, &end);maps[start][end] = maps[end][start] = 0;}prim();printf("%.2lf\n", ans);}return 0;}