P5837 [USACO19DEC]Milk Pumping G

知识点：枚举，最短路

这个题的正解应该是枚举+最短路，枚举每个边的流量，然后求起点到终点的最短路，当然小于枚举的流量的边其实就是不连通的，这样这个题就做出来了，但是一开始我写的是深搜，加了剪枝，用邻接矩阵存储，勉强过了，但是这个枚举+最短路确跑的快很多，明明复杂度也有1e7了，可能是因为实际中有很多断边的原因把，深搜的代码就不放了

#include <bits/stdc++.h>using namespace std;const int N = 2005;struct node {int x, d;node() {}node(int a, int b): x(a), d(b) {}bool operator < (const node &a) const {return d > a.d;}
};int tot, ver[N], c[N], f[N], nxt[N], head[N];
int n, m, a[N];void add(int x, int y, int t1, int t2) {ver[++tot] = y;c[tot] = t1; f[tot] = t2;nxt[tot] = head[x]; head[x] = tot;
}int bfs(int x) {priority_queue<node> q;q.push(node(1, 0));int vis[N] = {};while (!q.empty()) {node now = q.top(); q.pop();if (now.x == n) return now.d;if (vis[now.x]) continue;vis[now.x] = 1;for (int i = head[now.x]; i; i = nxt[i]) {if (f[i] >= x) q.push(node(ver[i], now.d + c[i]));}}return -1;
}int main() {cin >> n >> m;for (int i = 1; i <= m; i++) {int x, y, z;scanf("%d%d%d%d", &x, &y, &z, &a[i]);add(x, y, z, a[i]);add(y, x, z, a[i]);}double ans = 0;for (int i = 1; i <= m; i++) {int tmp = bfs(a[i]);if (tmp == -1) continue;ans = max(ans, 1.0 * a[i] / tmp);}cout << (int) (ans * 1e6);return 0;
}

P5837 [USACO19DEC]Milk Pumping G相关推荐

P2852 [USACO06DEC]Milk Patterns G
题目描述 Farmer John has noticed that the quality of milk given by his cows varies from day to day. On f ...
【树链剖分】Milk Visits G（luogu 5838）
正题 luogu 5838 题目大意给你一棵树,和若干查询,每次查询一条路径上是否有点的权值为x 解题思路离线处理,每次将树上权值为x的点附上1的值,然后询问就是求和,查询完后清零代码 #inc ...
[USACO19DEC]Moortal Cowmbat G 真牛快打
水帖... 题目描述 Bessie 玩格斗游戏真牛快打已经有很长时间了.然而,最近游戏开发者发布了一项更新,这迫使 Bessie 改变她的打法. 游戏总共使用 M 个按键,标记为前 M 个小写 ...
2020.6月做题记录
长期计划 SAM专题 date:2020.05.21-2020.06.01 基础类: Problem Finished P3804 [模板]后缀自动机 (SAM) √√√ SP1811 LCS - L ...
Hash（哈希）选做
洛谷 P3501 [POI2010]ANT-Antisymmetry 由题意得,"反对称"字符串长度一定为偶数. 原串正着 Hash,取反后的串倒着 Hash,然后枚举中间点,二分 ...
vue 组件数据共享_Vue共享组件
vue 组件数据共享 As a company, we sell experiences on many different sales channels, gotui.com, musement.c ...
文件上传之伪Ajax方式上传
From: <由 Windows Internet Explorer 8 保存> Subject: =?gb2312?B?zsS8/snPtKvWrs6xQWpheLe9yr3Jz7SrI ...
Milk Measurement
Milk Measurement 时间限制: 1 Sec 内存限制: 128 MB 题目描述 Each of Farmer John's cows initially produces G gallo ...
[USACO14MAR]Sabotage G
[USACO14MAR]Sabotage G 题目描述 Farmer John's arch-nemesis, Farmer Paul, has decided to sabotage Farmer ...

P5837 [USACO19DEC]Milk Pumping G

P5837 [USACO19DEC]Milk Pumping G相关推荐

最新文章

热门文章