poj 1201(差分约束+最长路)

差分约束：http://www.cppblog.com/menjitianya/archive/2015/11/19/212292.html

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

const int INF = 0xffffff;
struct Edge
{
int u,v,w,next;
Edge(){}
Edge(int u_,int v_,int w_)
{
u = u_;
v = v_;
w = w_;
}
}edges[200000];

int head[50010];
int d[50010];
int e = 0,maxnum = 0;
void addedge(int u,int v,int w)
{
edges[e] = Edge(u,v,w);
edges[e].next = head[u];
head[u] = e++;
}

int inq[50010];
void spfa()
{
queue<int> q;
while(!q.empty()) q.pop();
for(int i=0;i<=maxnum;i++) d[i] = -INF;
d[0] = 0;
memset(inq,0,sizeof(inq));
q.push(0);
inq[0] = 1;
while(!q.empty())
{
int u = q.front(); q.pop();
inq[u]--;
for(int i=head[u];i!=-1;i=edges[i].next)
{
int v = edges[i].v;
if(d[v] < d[u] + edges[i].w)
{
d[v] = d[u] + edges[i].w;
if(!inq[v])
{
inq[v]++;
q.push(v);
}
}
}
}
}

int main()
{
int n,u,v,w;
scanf("%d",&n);
memset(head,-1,sizeof(head));
maxnum = 0;
e = 0;
//Sbi - Sai >= ci
//Si - Si-1 >= 0
//Si-1 - Si >= -1
while(n--)
{
scanf("%d%d%d",&u,&v,&w);
if(v+1 > maxnum) maxnum = v+1;//整体+1了，所以是v+1
addedge(u,v+1,w); //整体+1
}

//0 <= d[i] - d[i-1] <= 1（即第i个数选还是不选）
for(int i=0;i<=maxnum;i++)
{
addedge(i,i+1,0);
addedge(i+1,i,-1);
}
spfa();
printf("%d\n",d[maxnum]);
return 0;
}