POJ 3159 Candies(差分约束系统)

//差分约束系统
//建立关系十分简单，SPFA求到终点的距离
//但这一题十分奇怪，用队列就TLE,用栈就不会，真奇怪~
#include<iostream>
#include<stack>
#define MAXN 30005
#define MAXM 150000
#define INF 1000000000
using namespace std;
int N,M,m,u,v,w;
bool inq[MAXN];
int dis[MAXN];
int head[MAXN],next[MAXM],V[MAXM],W[MAXM];
inline void addEdge(int u,int v,int w)
{
V[m] = v;
W[m] = w;
next[m] = head[u];
head[u] = m++;
}
void buildGraph()
{
m = 0;
scanf("%d%d",&N,&M);
memset(head,-1,sizeof(head));
while(M--)
{
scanf("%d%d%d",&u,&v,&w);
addEdge(u,v,w);
}
}
int SPFA()
{
for(int i = 2;i <= N;++i)	dis[i] = INF;
dis[1] = 0;
stack<int> q;//用堆栈来做就不会超时了
q.push(1);
inq[1] = 1;
while(!q.empty())
{
int u = q.top();	q.pop();
inq[u] = 0;
for(int e = head[u];e != -1;e = next[e])
{
if(dis[u] + W[e] < dis[V[e]])
{
dis[V[e]] = dis[u] + W[e];
if(!inq[V[e]])
{
q.push(V[e]);
inq[V[e]] = 1;
}
}
}
}
return dis
;//返回终点的距离就是答案
}
int main()
{
buildGraph();
printf("%d/n",SPFA());
return 0;
}