图论 - 树论 - 生成树 - Prim

图论 - 树论 - 生成树 - Prim

题目链接：https://www.luogu.org/problem/P3366

代码：

#include <bits/stdc++.h>

using namespace std;

const int N = 5010;

const int M = 200010;

int n, m, dis[N], ans;

int tot, head[N], val[M << 1], nxt[M << 1] ,to[M << 1];

bool vis[N];

void add(int x, int y, int z) {
	to[ ++ tot] = y;
	val[tot] = z;
	nxt[tot] = head[x];
	head[x] = tot;
}

void Prim() {
	memset(dis, 0x3f, sizeof dis);
	memset(vis, 0, sizeof vis);
	dis[1] = 0;
	for (int i = 1; i <= n; i ++ ) {
		int tmp = 1 << 30, k;
		for (int j = 1; j <= n; j ++ ) {
			if (vis[j] == 0 && dis[j] < tmp) {
				tmp = dis[j];
				k = j;
			}
		}
		vis[k] = 1;
		ans += dis[k];
		for (int j = head[k]; j; j = nxt[j]) {
			if (vis[to[j]] == 0 && dis[to[j]] > val[j]) {
				dis[to[j]] = val[j];
			}
		}
	}
}

int main() {
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= m; i ++ ) {
		int x, y, z;
		scanf("%d%d%d", &x, &y, &z);
		add(x, y, z);
		add(y, x, z);
	}
	Prim();
	printf("%d\n", ans);
	return 0;
}