zoukankan      html  css  js  c++  java
  • (简单) POJ 3169 Layout,差分约束+SPFA。

      Description

      Like everyone else, cows like to stand close to their friends when queuing for feed. FJ has N (2 <= N <= 1,000) cows numbered 1..N standing along a straight line waiting for feed. The cows are standing in the same order as they are numbered, and since they can be rather pushy, it is possible that two or more cows can line up at exactly the same location (that is, if we think of each cow as being located at some coordinate on a number line, then it is possible for two or more cows to share the same coordinate).

      Some cows like each other and want to be within a certain distance of each other in line. Some really dislike each other and want to be separated by at least a certain distance. A list of ML (1 <= ML <= 10,000) constraints describes which cows like each other and the maximum distance by which they may be separated; a subsequent list of MD constraints (1 <= MD <= 10,000) tells which cows dislike each other and the minimum distance by which they must be separated.

      Your job is to compute, if possible, the maximum possible distance between cow 1 and cow N that satisfies the distance constraints.
     
      题意就是 Xi-Xj<c 然后求 Xn-X1 的最大值,差分约束问题。。。
      建图然后SPFA 就好。。。
     
    代码如下:
    #include <stdio.h>
    #include <string.h>
    #include <iostream>
    #include <algorithm>
    #include <vector>
    #include <queue>
    #include <set>
    #include <map>
    #include <string>
    #include <math.h>
    #include <stdlib.h>
    #include <time.h>
        
    using namespace std;
    
    const int MaxN=1010;
    const int MaxM=30100;
    const int INF=1000000009;
    
    struct Edge
    {
        int to,next,cost;
    };
    
    Edge E[MaxM];
    int head[MaxN],Ecou;
    
    bool vis[MaxN];
    int couNode[MaxN];
    
    void init(int N)
    {
        Ecou=0;
        for(int i=1;i<=N;++i)
        {
            head[i]=-1;
            couNode[i]=0;
            vis[i]=0;
        }
    }
    
    void addEdge(int u,int v,int w)
    {
        E[Ecou].to=v;
        E[Ecou].cost=w;
        E[Ecou].next=head[u];
        head[u]=Ecou++;
    }
    
    bool SPFA(int lowcost[],int N,int start)
    {
        int t,v;
        queue <int> que;
    
        for(int i=1;i<=N;++i)
            lowcost[i]=INF;
        lowcost[start]=0;
    
        que.push(start);
        couNode[start]=1;
        vis[start]=1;
    
        while(!que.empty())
        {
            t=que.front();
            que.pop();
    
            vis[t]=0;
    
            for(int i=head[t];i!=-1;i=E[i].next)
            {
                v=E[i].to;
                
                if(lowcost[v]>lowcost[t]+E[i].cost)
                {
                    lowcost[v]=lowcost[t]+E[i].cost;
    
                    if(!vis[v])
                    {
                        vis[v]=1;
                        couNode[v]+=1;
                        que.push(v);
    
                        if(couNode[v]>N)
                            return 0;
                    }
                }
            }
        }
    
        return 1;
    }
    
    int ans[MaxN];
    
    int main()
    {
        //freopen("in.txt","r",stdin);
        //freopen("out.txt","w",stdout);
        
        int N,ML,MD;
        int a,b,c;
    
        scanf("%d %d %d",&N,&ML,&MD);
    
        init(N);
    
        for(int i=1;i<=ML;++i)
        {
            scanf("%d %d %d",&a,&b,&c);
    
            addEdge(a,b,c);
        }
    
        for(int i=1;i<=MD;++i)
        {
            scanf("%d %d %d",&a,&b,&c);
    
            addEdge(b,a,-c);
        }
    
        for(int i=1;i<=N-1;++i)
            addEdge(i+1,i,0);
    
        if(!SPFA(ans,N,1))
            printf("-1
    ");
        else if(ans[N]!=INF)
            printf("%d
    ",ans[N]);
        else
            printf("-2
    ");
    
        return 0;
    }
    View Code
  • 相关阅读:
    微信公众号对接配置
    ASP.NET MVC5+EF6+EasyUI 后台管理系统(89)-国际化,本地化,多语言应用
    Nacos安装教程
    IDEA 中创建SpringBoot 父子模块
    解决死锁之路(终结篇)
    CentOS安装node和npm
    CentOS安装RabbitMQ
    在LibreOffice中插入代码
    PowerShell查找程序路径
    使用命令行调用控制面板的选项
  • 原文地址:https://www.cnblogs.com/whywhy/p/4337864.html
Copyright © 2011-2022 走看看