In HDU, you have to run along the campus for 24 times, or you will fail in PE. According to the rule, you must keep your speed, and your running distance should not be less than K meters.
There are 4 checkpoints in the campus, indexed as p1,p2,p3 and p4.
Every time you pass a checkpoint, you should swipe your card, then the
distance between this checkpoint and the last checkpoint you passed will
be added to your total distance.
The system regards these 4 checkpoints as a circle. When you are at checkpoint pi, you can just run to pi−1 or pi+1(p1 is also next to p4). You can run more distance between two adjacent checkpoints, but only the distance saved at the system will be counted.
Checkpoint p2
is the nearest to the dormitory, Little Q always starts and ends
running at this checkpoint. Please write a program to help Little Q find
the shortest path whose total distance is not less than K
1 2000 600 650 535 380Sample Output
2165
Hint
The best path is 2-1-4-3-2.
OJ-ID：
hdu-6071
author：
Caution_X
date of submission：
20191024
tags：
dp+dijkstra
description modelling：
有四个点1，2，3，4形成环1-2-3-4-1，四条边的权值表示距离，问能否找到一条路径从点2出发回到点2并且权值之和大于K
major steps to solve it：
w=min(d1,d2)，其中d1是1，2之间的距离，d2是2，3之间的距离
假设有符合条件的最小权值和P，那么就会有最佳的P-w
设dp[i][j]:=从2出发到达i点时的最小权值和，其中j是权值和%(2*w)，之所以%(2*w)是因为从2出发再回到2权值和最少2*w
同样是从2到达i点，不同的j表示不同的路径，若j相同但是从2到i的权值和不同，则选择权值和小的
（1）dijkstra更新dp[i][j]
（2）判断dp[2][j]是否大于K，若小于K则不足之处用w填充
AC code:
#include<bits/stdc++.h> using namespace std; typedef long long ll; typedef pair<ll, int> P; const ll INF = 1e18; const int MAXN = 6e4 + 10; vector<P> G[MAXN]; ll d[5][MAXN]; void dijkstra(ll w, int s) { for(int i = 1; i <= 4; i++) { fill(d[i], d[i] + w, INF); } priority_queue<P, vector<P>, greater<P> >q; q.push(P(0, s)); d[s][0] = 0; while(!q.empty()) { P p = q.top(); q.pop(); int v = p.second; if(p.first > d[v][p.first % w]) continue; for(int i = 0; i < (int)G[v].size(); i++) { P e = G[v][i]; ll dist = e.first + d[v][p.first % w]; if(dist < d[e.second][dist % w]) { d[e.second][dist % w] = dist; q.push(P(dist, e.second)); } } } } int main() { int T; cin >> T; while(T--) { memset(G, 0, sizeof G); ll K, d1, d2, d3, d4; cin >> K >> d1 >> d2 >> d3 >> d4; G[1].push_back(P(d1, 2)); G[2].push_back(P(d1, 1)); G[2].push_back(P(d2, 3)); G[3].push_back(P(d2, 2)); G[3].push_back(P(d3, 4)); G[4].push_back(P(d3, 3)); G[4].push_back(P(d4, 1)); G[1].push_back(P(d4, 4)); ll w = 2 * min(d1, d2); dijkstra(w, 2); ll ans = INF; for(ll i = 0; i < w; i++) { if(d[2][i] >= K) { ans = min(ans, d[2][i]); } else { ll nd = K - d[2][i]; ans = min(ans, d[2][i] + nd / w * w + (nd % w > 0) * w); } } cout << ans << endl; } return 0; }
原文：https://www.cnblogs.com/cautx/p/11735479.html