P1546 [USACO3.1]最短网络 Agri-Net TJ

题目链接

思路

最小生成树模板题。
(Prim)。

代码

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int MAXN = 2e2 + 10;
struct node {
	int next ,to ,val;
}edge[MAXN * MAXN]; 
int head[MAXN] ,cnt = 0;
void add (int from ,int to ,int val) {
	edge[++ cnt].next = head[from];
	head[from] = cnt;
	edge[cnt].to = to;
	edge[cnt].val = val;
}
int n;
int dis[MAXN] ,vis[MAXN];
int prim (int cur) {
	int ans = 0;
	memset (dis ,0x3f ,sizeof (dis));
	memset (vis ,0 ,sizeof (vis));
	dis[cur] = 0;
	vis[cur] = 1;
	for (int q = head[cur];~ q;q = edge[q].next) {
		dis[edge[q].to] = edge[q].val;
	}
	for (int q = 1;q < n;++ q) {
		int minl = 0x3f3f3f3f ,ind;
		for (int w = 1;w <= n;++ w) {
			if (minl > dis[w] && ! vis[w]) {
				minl = dis[w];
				ind = w;
			}
		}
		ans += dis[ind];
		vis[ind] = 1;
		for (int q = head[ind];~ q;q = edge[q].next) {
			int v = edge[q].to;
			if (! vis[v])
				dis[v] = min (dis[v] ,edge[q].val);
		}
	}
	return ans;
}
int main () {
	memset (head ,-1 ,sizeof (head));
	scanf ("%d",&n);
	int x;
	for (int q = 1;q <= n;++ q) {
		for (int w = 1;w <= n;++ w) {
			scanf ("%d",&x);
			if (x != 0) add (q ,w ,x) ,add (w ,q ,x);
		}
	}
	printf ("%d
",prim (1));
	return 0;
}