HDU 4940 destroy Transportation System (graph theory)

What I thought at the time of this question was that if the sum of the D value of a vertex is greater than the sum of the D + B value, we can. That's it. However, there is another way to solve the problem, which seems a little difficult. In the future, make up that practice.

Destroy Transportation System Time Limit: 2000/1000 MS (Java/others) memory limit: 131072/131072 K (Java/Others)
Total submission (s): 289 accepted submission (s): 181


Problem descriptiontom is a commander, his task is destroying his enemy's transportation system.

Let's represent his enemy's transportation system as a simple directed graph G with N nodes and m edges. each node is a city and each directed edge is a directed Road. each edge from node u to node v is associated with two values D and B, D is the cost to destroy/remove such edge, B is the cost to build an undirected edge between u and v.

His enemy can deliver supplies from City U to city V if and only if there is a directed path from u to v. at first they can deliver supplies from any city to any other cities. so the graph is a stronugly-connected graph.

He will choose a non-empty proper subset of cities, let's denote this set as S. let's denote the complement set of S as T. he will command his soldiers to destroy all the edges (u, v) that u belongs to set S and v belongs to set T.

To destroy an edge, he must pay the related cost D. The total cost he will pay is X. You can use this formula to calculate X:

After that, all the edges from S to t are destroyed. in order to deliver huge number of supplies from S to T, his enemy will change all the remained directed edges (u, v) that u belongs to set T and V belongs to set S into undirected edges. (surely, those edges exist because the original graph is stronugly-connected)

To change an edge, they must remove the original directed edge at first, whose cost is d, then they have to build a new undirected edge, whose cost is B. the total cost they will pay is Y. you can use this formula to calculate Y:

At last, if y> = x, Tom will achieve his goal. but Tom is so lazy that he is unwilling to take a cup of time to choose a set S to make y> = x, he hope to choose set S randomly! So he asks you if there is a set S, such that Y <X. if such set exists, he will feel unhappy, because he must choose set S carefully, otherwise he will become very happy.
Inputthere are multiply test cases.

The first line contains an integer T (t <= 200), indicates the number of cases.

For each test case, the first line has two numbers N and M.

Next m lines describe each edge. Each line has four numbers U, V, D, B.
(2 = <n <= 200, 2 = <m <= 5000, 1 = <u, v <= N, 0 = <D, B <= 100000)

The meaning of all characters are described above. It is guaranteed that the input graph is stronugly-connected.
Outputfor each case, output "case # X:" First, X is the case number starting from 1.if such set doesn't exist, print "happy", else print "unhappy ".
Sample Input

23 31 2 2 22 3 2 23 1 2 23 31 2 10 22 3 2 23 1 2 2

 
Sample output

Case #1: happyCase #2: unhappyHintIn first sample, for any set S, X=2, Y=4. In second sample. S= {1}, T= {2, 3}, X=10, Y=4.

#include <algorithm>#include <iostream>#include <stdlib.h>#include <string.h>#include <iomanip>#include <stdio.h>#include <string>#include <queue>#include <cmath>#include <stack>#include <map>#include <set>#define eps 1e-10///#define M 1000100#define LL __int64///#define LL long long///#define INF 0x7ffffff#define INF 0x3f3f3f3f#define PI 3.1415926535898#define zero(x) ((fabs(x)<eps)?0:x)const int maxn = 2010;using namespace std;struct node{    int x, y;} f[maxn];int main(){    int T;    cin >>T;    int Case = 1;    while(T--)    {        int n, m;        cin >>n>>m;        int x, y;        int d, b;        for(int i = 0; i <= n; i++) f[i].x = f[i].y = 0;        for(int i = 0; i < m; i++)        {            scanf("%d %d %d %d",&x, &y, &d, &b);            f[x].y += d;            f[y].x += (d+b);        }        int flag = 0;        for(int i = 1; i <= n; i++)        {            if(f[i].x < f[i].y)            {                flag = 1;                break;            }        }        cout<<"Case #"<<Case++<<": ";        if(flag) cout<<"unhappy"<<endl;        else cout<<"happy"<<endl;    }    return 0;}