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  • HDU 3592 World Exhibition(线性差分约束,spfa跑最短路+判断负环)

    World Exhibition

    Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
    Total Submission(s): 2162    Accepted Submission(s): 1063


    Problem Description
    Nowadays, many people want to go to Shanghai to visit the World Exhibition. So there are always a lot of people who are standing along a straight line waiting for entering. Assume that there are N (2 <= N <= 1,000) people numbered 1..N who are standing in the same order as they are numbered. It is possible that two or more person line up at exactly the same location in the condition that those visit it in a group.

    There is something interesting. Some 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 X (1 <= X <= 10,000) constraints describes which person like each other and the maximum distance by which they may be separated; a subsequent list of Y constraints (1 <= Y <= 10,000) tells which person 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 person 1 and person N that satisfies the distance constraints.
     
    Input
    First line: An integer T represents the case of test.

    The next line: Three space-separated integers: N, X, and Y.

    The next X lines: Each line contains three space-separated positive integers: A, B, and C, with 1 <= A < B <= N. Person A and B must be at most C (1 <= C <= 1,000,000) apart.

    The next Y lines: Each line contains three space-separated positive integers: A, B, and C, with 1 <= A < B <= C. Person A and B must be at least C (1 <= C <= 1,000,000) apart.
     
    Output
    For each line: A single integer. If no line-up is possible, output -1. If person 1 and N can be arbitrarily far apart, output -2. Otherwise output the greatest possible distance between person 1 and N.
     
    Sample Input
    1 4 2 1 1 3 8 2 4 15 2 3 4
     
    Sample Output
    19
     
    Author
    alpc20
     
    Source
     
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    分析:
    负环的定义:
    有向图中存在一个环,其权值和为负数
    这题跟poj3169一模一样
    解析:
     
    code:
    #include<stdio.h>
    #include<iostream>
    #include<math.h>
    #include<string.h>
    #include<set>
    #include<map>
    #include<list>
    #include<math.h>
    #include<queue>
    #include<algorithm>
    using namespace std;
    typedef long long LL;
    #define INF 9999999999
    #define me(a,x) memset(a,x,sizeof(a))
    int mon1[13]= {0,31,28,31,30,31,30,31,31,30,31,30,31};
    int mon2[13]= {0,31,29,31,30,31,30,31,31,30,31,30,31};
    int dir[4][2]= {{0,1},{0,-1},{1,0},{-1,0}};
    
    int getval()
    {
        int ret(0);
        char c;
        while((c=getchar())==' '||c=='
    '||c=='
    ');
        ret=c-'0';
        while((c=getchar())!=' '&&c!='
    '&&c!='
    ')
            ret=ret*10+c-'0';
        return ret;
    }
    void out(int a)
    {
        if(a>9)
            out(a/10);
        putchar(a%10+'0');
    }
    
    #define max_v 1005
    struct node
    {
        int v;
        LL w;
        node(int vv=0,LL ww=0):v(vv),w(ww) {}
    };
    LL dis[max_v];
    int vis[max_v];
    int cnt[max_v];
    vector<node> G[max_v];
    queue<int> q;
    
    void init()
    {
        for(int i=0; i<max_v; i++)
        {
            G[i].clear();
            dis[i]=INF;
            vis[i]=0;
            cnt[i]=0;
        }
        while(!q.empty())
            q.pop();
    }
    
    int spfa(int s,int n)
    {
        vis[s]=1;
        dis[s]=0;
        q.push(s);
        cnt[s]++;
    
        while(!q.empty())
        {
            int u=q.front();
            q.pop();
            vis[u]=0;
    
            for(int j=0; j<G[u].size(); j++)
            {
                int v=G[u][j].v;
                LL w=G[u][j].w;
    
                if(dis[v]>dis[u]+w)
                {
                    dis[v]=dis[u]+w;
                    if(vis[v]==0)
                    {
                        q.push(v);
                        cnt[v]++;
                        vis[v]=1;
    
                        if(cnt[v]>n)
                            return 0;
                    }
                }
            }
        }
        return 1;
    }
    int f(int u,int v)
    {
        for(int j=0; j<G[u].size(); j++)
        {
            if(G[u][j].v==v)
                return 0;
        }
        return 1;
    }
    int main()
    {
        int n,a,b;
        int t;
        scanf("%d",&t);
        while(t--)
        {
            scanf("%d %d %d",&n,&a,&b);
            init();
            int x,y,w;
            while(a--)
            {
                scanf("%d %d %d",&x,&y,&w);
                if(f(x,y))
                    G[x].push_back(node(y,w));
            }
            while(b--)
            {
                scanf("%d %d %d",&x,&y,&w);
                if(f(y,x))
                    G[y].push_back(node(x,-w));
            }
            int flag=spfa(1,n);
            if(flag==0)
            {
                printf("-1
    ");
            }
            else if(dis[n]<INF)
            {
                printf("%lld
    ",dis[n]);
            }
            else
            {
                printf("-2
    ");
            }
        }
        return 0;
    }
     
    心之所向,素履以往
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  • 原文地址:https://www.cnblogs.com/yinbiao/p/10001901.html
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