HDU5988 Coding Contest(费用流)

2016青岛现场赛的一题，由于第一次走过不会产生影响，需要拆点，不过比赛时没想到，此外还有许多细节要注意，如要加eps,时间卡得较紧要注意细节优化等

#include <iostream>
#include <cstring>
#include <queue>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <cstring>
#include <vector>
using namespace std;
const int N = 108, M = 50000;
const int INF = 1e9;
const double eps = 1e-7;
int q[1000000];
struct Node{
	int u, v, cap;
	double cost;
	int next;
}edge[M];//有向图，u到v的容量，费用
int tot;
int head[N], pre[N], path[N];
double dis[N];
bool inq[N];

void init(){
	tot = 0;
	memset(head, -1, sizeof(head));
}

void add(int u, int v, int cap, double cost){
    edge[tot].u = u;
	edge[tot].v = v;
	edge[tot].cap = cap;
	edge[tot].cost = cost;
	edge[tot].next = head[u];
	head[u] = tot++;
	edge[tot].u = v;
	edge[tot].v = u;
	edge[tot].cap = 0;
	edge[tot].cost = -cost;
	edge[tot].next = head[v];
	head[v] = tot++;
}

bool SPFA(int st, int des){
	memset(inq, 0, sizeof(inq));
	fill(dis, dis + des + 2, INF);
	memset(pre, -1, sizeof(pre));
	int front = 0, rear = 0;
	q[rear++] = st;
	dis[st] = 0;
	inq[st] = true;
	while(front < rear){
		int u = q[front++];

		inq[u] = false;
		for(int i = head[u]; ~i; i = edge[i].next){
			int v = edge[i].v;
			if(edge[i].cap > 0 && dis[v] > dis[u] + edge[i].cost + eps){
				dis[v] = dis[u] + edge[i].cost;
				pre[v] = u;
				path[v] = i;
				if(!inq[v]){
					inq[v] = true;
					q[rear++] = v;
				}
			}
		}
	}
	return pre[des] != -1;
	//return dis[des] + eps < INF;
}

double EdmondsKarp(int st, int des){
	double mincost = 0, flow = 0;
	while(SPFA(st, des)){
		int f = INF;
		for(int i = des; i != st; i = pre[i]){
            if(f > edge[path[i]].cap){
                f = edge[path[i]].cap;
            }
		}
		for(int i = des; i != st; i = pre[i]){
			edge[path[i]].cap -= f;
			edge[path[i]^1].cap += f;
		}
		mincost += f * dis[des];
		flow += f;
	}
	return mincost;
}
int main(){
	int t;
	cin >>t;
	while(t--){
		int n, m;
		scanf("%d %d", &n, &m);
		init();
		int st = 0, des = n + 1;
		for(int i = 1; i <= n; i++){
			int si, bi;
			scanf("%d %d", &si, &bi);
			if(si > bi){
				add(st, i, si - bi, 0.0);
			}else if(si < bi){
				add(i, des, bi - si, 0.0);
			}
		}
		while(m--){
			int u, v, c;
			double p;
			scanf("%d %d %d %lf", &u, &v, &c, &p);
			if(c > 0){
                add(u, v, 1, 0);
                if(c > 1){
                    add(u, v, c - 1, -log10(1 - p));
                }
			}
		}
		printf("%.2f\n", 1.0 - pow(10.0, -EdmondsKarp(st, des)));

	}
	return 0;
}