poj1201

http://blog.csdn.net/rookie_algo/article/details/7833801

和1716一樣，差分約束，列出以下式子：

1、s[bi]-s[ai-1]>=2

2、s[i+1]-s[i]>=0

3、s[i+1]-s[i]<=1

#include<iostream>
using namespace std;
const int MAXN = 50001;
struct edge
{
	int u,v,w;
}vetex[MAXN];
int dis[MAXN];
int ulim,dlim;
int main()
{
	int n;
	while(cin>>n)
	{
		ulim = -1;dlim = MAXN;
		for(int i=1;i!=n+1;i++)
		{
			cin>>vetex[i].u;
			cin>>vetex[i].v;
			++vetex[i].v;
			cin>>vetex[i].w;
			dis[i] = 0;
			if(ulim<vetex[i].v)
			{
				ulim=vetex[i].v;
			}
			if(dlim>vetex[i].u)
			{
				dlim=vetex[i].u;
			}
		}
		bool flag = true;
		while(flag)
		{
			flag = false;
			for(int i=1;i!=n+1;i++)
			{
				if(dis[vetex[i].u]>dis[vetex[i].v]-vetex[i].w)
				{
					dis[vetex[i].u]=dis[vetex[i].v]-vetex[i].w;
					flag = true;
				}
			}
			for(int i=dlim;i!=ulim+1;i++)
			{
				if(dis[i+1]>dis[i]+1)
				{
					dis[i+1] = dis[i]+1;
					flag = true;
				}
			}
			for(int i=ulim;i!=dlim-1;i--)
			{
				if(dis[i]>dis[i+1])
				{
					dis[i] = dis[i+1];
					flag = true;
				}
			}
		}
		cout<<dis[ulim]-dis[dlim]<<endl;
	}
	return 0;
}