HDOJ 5483 Nux Walpurgis

最新推荐文章于 2021-04-29 13:40:27 发布

yysys

最新推荐文章于 2021-04-29 13:40:27 发布

阅读量459

点赞数

CC 4.0 BY-SA版权

本文链接：https://blog.youkuaiyun.com/blankcqk/article/details/48806669

本文介绍了一种算法，该算法首先构建图的最小生成树，然后通过深度优先搜索判断树中的每条边是否可以被安全删除。具体实现包括 Prim 算法构建最小生成树、DFS 检查边的有效性等步骤。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

先做出最小生成树,然后对每个点dfs判断树边是否可删.....

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;

const int maxn = 3005;
const int maxm = 6005;
const int INF = 0x3f3f3f3f;

struct Edge
{
	int v;
	Edge *next;
}E[maxm], *H[maxn], *edges;

int g[maxn][maxn];
int is[maxn][maxn];
int lowc[maxn];
int pre[maxn];
int dis[maxn];
int vis[maxn];
int n;

void init()
{
	edges = E;
	memset(H, 0, sizeof H);
	memset(is, 0, sizeof is);
}

void addedges(int u, int v)
{
	edges->v = v;
	edges->next = H[u];
	H[u] = edges++;
}

void Prim()
{
	memset(vis, 0, sizeof vis);
	vis[1] = true;
	for(int i = 1; i <= n; i++) lowc[i] = g[1][i], pre[i] = 1;
	for(int i = 1; i < n; i++) {
		int minc = INF;
		int p = -1, t = -1;
		for(int j = 1; j <= n; j++) if(!vis[j] && minc > lowc[j]) {
			minc = lowc[j];
			p = j;
			t = pre[j];
		}
		vis[p] = true;
		for(int j = 1; j <= n; j++) if(!vis[j] && lowc[j] > g[p][j]) {
			lowc[j] = g[p][j];
			pre[j] = p;
		}
		is[p][t] = is[t][p] = true;
	}
	
}

void dfs(int u, int fa)
{
	for(Edge *e = H[u]; e; e = e->next) if(e->v != fa) {
		int v = e->v;
		dfs(e->v, u);
		dis[u] = min(dis[u], dis[v]);
	}
	if(g[fa][u] >= dis[u]) is[fa][u] = is[u][fa] = 0;
}

void debug()
{
	for(int i = 1; i <= n; i++) {
		for(int j = 1; j <= n; j++)
			printf("%d ", is[i][j]);
		printf("\n");
	}
}

void work()
{
	scanf("%d", &n);
	for(int i = 1; i < n; i++)
		for(int j = 1; j <= n - i; j++) {
			int x;
			scanf("%d", &x);
			g[i][i+j] = g[i+j][i] = x;
		}
	for(int i = 1; i <= n; i++) g[i][i] = 0;
	
	Prim();
	
	for(int i = 1; i <= n; i++)
		for(int j = 1; j <= n; j++)
			if(is[i][j]) addedges(i, j);
	for(int i = 1; i <= n; i++) g[0][i] = INF;
	for(int i = 1; i <= n; i++) {
		for(int j = 1; j <= n; j++) {
			if(is[i][j]) dis[j] = INF;
			else dis[j] = g[i][j];
		}
		dfs(i, 0);
	}
	int ans = 0;
	for(int i = 1; i <= n; i++)
		for(int j = 1; j <= n; j++)
			ans += is[i][j];
	printf("%d\n", ans / 2);
}

int main()
{
	//freopen("data", "r", stdin);
	int _;
	scanf("%d", &_);
	while(_--) {
		init();		
		work();
	}
	
	return 0;
}