zoj 2770 Burn the Linked Camp 差分约束

       设x[i] 为第i个营的人数，s[i] = x[1] + x[2] + … + x[i], s[0] = 0

       则对于题目

       Ci 有： 0 <= s[i] – s[i-1] <= Ci

       i, j, k有： s[j] – s[i-1] >= k

       还有： s[i] >= 0 (1 <= i <= n) , 即 s[i] – s[0] >= 0

       这题求最小值，以0为源点求最长路

 

#include<iostream>
#include <queue>
#include <cstdio>
#include <cstring>
using namespace std;

const int MAX = 20000;
const int INF = 1000000000;
const int N = 10000;

struct Node
{
	int v;
	int cost;
	int next;
};

Node node[MAX];
int adj[N];
int d[N];
bool in_q[N];
int cnt[N];
int size;
int n, m;

void add_edge(int u, int v, int cost)
{
	node[size].v = v;
	node[size].cost = cost;
	node[size].next = adj[u];
	adj[u] = size++;
}

bool spfa()
{
	queue<int> Q;

	memset(in_q, false, sizeof(in_q));
	memset(cnt, 0, sizeof(cnt));
	for (int i = 0; i <= n; i++)
		d[i+1] = -INF;
		
	int u, v, w;
	d[0] = 0;
	Q.push(0);
	in_q[0] = true;

	while (!Q.empty())
	{
		u = Q.front();
		Q.pop();
		in_q[u] = false;

		for (int i = adj[u]; i != -1; i = node[i].next)
		{
			v = node[i].v;
			w = node[i].cost;

			if (d[v] < d[u] + w)
			{
				d[v] = d[u] + w;
				if (!in_q[v])
				{
					in_q[v] = true;
					Q.push(v);
				}

				if (++cnt[v] > n) return false;
			}
		}
	}

	return true;	
}

int main()
{
	int u, v, w;

	while (cin >> n >> m)
	{
		size = 0;
		for (int i = 0; i <= n+1; i++)
			adj[i] = -1;

		int c;
		for (int i = 1; i <= n; i++)
		{
			scanf("%d", &c);
			add_edge(i-1, i, 0);
			add_edge(i, i-1, -c);
		}
		
		for (int i = 1; i <= n; i++)
			add_edge(0, i, 0);

		for (int i = 0; i < m; i++)
		{
			scanf("%d%d%d", &u, &v, &w);
			add_edge(u-1, v, w);		
		}

		if (spfa())
		{
			printf("%d\n", d[n]);
		}
		else
			printf("Bad Estimations\n");
	}
	return 0;
}