题目 两眼题 二分一个\(lim\),然后跑最短路(边权\(\le lim\)的边长度为\(0\),\(>lim\)的长度为\(1\)),然后判断\(dis_{1,n}\le k\). #include<bits/stdc++.h> #define pi pair<int,int> #define pb push_back using namespace std; int read(){int x;scanf("%d",&x);return x;}…

题意描述 在无向图中求一条从 \(1\) 到 \(N\) 的路径,使得路径上第 \(K+1\) 大的边权最小. 等等,最大的最小...如此熟悉的字眼,难道是 二分答案. 下面进入正题. 算法分析 没错就是酱紫,二分这个第 \(K+1\) 大的边权的值,设这条边的边权为 \(val\) 那么: \[ edge[i]=\left\{ \begin{array}{rcl} 0 & & {edge[i] \leq val}\\ 1 & & {edge[i] > val}\ \…

P1948 [USACO08JAN]电话线Telephone Lines 题意 题目描述 Farmer John wants to set up a telephone line at his farm. Unfortunately, the phone company is uncooperative, so he needs to pay for some of the cables required to connect his farm to the phone system. Ther…

嘟嘟嘟 题意概括一下,就是在无向图上求一条1到n的路径,使路径上第k + 1大的边权尽量小. 考虑dp,令dp[i][j] 表示走到节点 i,路线上有 j 条电话线免费时,路径上最贵的电缆花费最小是多少.则对于一条从u到v,长度为w的边,转移方程是: 1.这条电缆要付费:dp[v][p] = min(dp[v][p], max(dp[u][p], w)) 2.这条电缆免费:dp[v][p + 1] = min(dp[v][p +1], dp[u][p]) 不过这是在图上dp,转移不能保证无后效性…

这道题目有两种解法: 1.将每个点视为一个二元组(x,p),表示从起点到x有p条路径免费,相当于构建了一张分层图,N*k个节点,P*k条边.在这张图上用优先队列优化的SPFA算法求解,注意这里的d数组存的不是最短路径,而是路径中边权最大的值,最终答案就是min(d[n][j]),0<=j<=k . 1 #include<bits/stdc++.h> 2 using namespace std; 3 const int N=1005,M=20005; 4 int head[N],to…

P1948 [USACO08JAN]电话线Telephone Lines 题目描述 Farmer John wants to set up a telephone line at his farm. Unfortunately, the phone company is uncooperative, so he needs to pay for some of the cables required to connect his farm to the phone system. There a…

P1948 [USACO08JAN]电话线Telephone Lines 题目描述 Farmer John wants to set up a telephone line at his farm. Unfortunately, the phone company is uncooperative, so he needs to pay for some of the cables required to connect his farm to the phone system. There a…

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洛谷 P1948 [USACO08JAN]电话线Telephone Lines https://www.luogu.org/problem/P1948 JDOJ 2556: USACO 2008 Jan Silver 3.Telephone Lines https://neooj.com/oldoj/problem.php?id=2556 题目描述 Farmer John wants to set up a telephone line at his farm. Unfortunately, t…

1614: [Usaco2007 Jan]Telephone Lines架设电话线 Time Limit: 5 Sec  Memory Limit: 64 MBSubmit: 892  Solved: 399[Submit][Status] Description Farmer John打算将电话线引到自己的农场,但电信公司并不打算为他提供免费服务.于是,FJ必须为此向电信公司支付一定的费用. FJ的农场周围分布着N(1 <= N <= 1,000)根按1..N顺次编号的废弃的电话线杆,任意两…