POJ 3159 Candies or difference constraint (stack SPFA)

Http://poj.org/problem? Id = 3159

Question:

N Children divide candy. You must satisfy their requirements (a B x means B cannot exceed a x Candy) and the gap between Candy numbers 1 and n is the biggest.

Ideas:

Well, let me reveal it first. The first day is a candy-sharing child, the squad leader! (Bulletin Board private hatred..., bully the children on the N number ~ Okay, I'm kidding)

Well, this question requires the shortest path. Why is it the shortest? You used to play longest ~

Because this question requires the greatest. The triangle inequalities in the figure are: d [v]-d [u] <= w (u, v); d [v] <= d [u] + w (u, v); that is, the relaxation condition is: if (d [v]> d [u] + w (u, v )) d [v] <= d [u] + w (u, v); through constant relaxation, the value of d keeps decreasing until all conditions are met, that is to say, when conditions are met, it is the greatest ~

Create a diagram, B-a <= x and then spfa, but the question is actually stuck in the queue .. Look at the discuss people use stack, and then I changed it. That's it ......

In addition, super source points cannot be created for this question.

Set the candy assigned by the first child to s [I], then s [I]> = 0

The above is B-a <= x. Because this is the shortest path, we need to change it to a smaller number, that is,-s [I] <= 0, then, if you add a vertex, for example, 0, it should be from I to 0, and it will be useless ....

#include
 
  #include
  
   #include
   
    using namespace std;const int MAXN=30000+10;const int MAXM=350000;const int INF=-999999;int n,m,head[MAXN],len,dis[MAXN];bool vis[MAXN];struct edge{int to,val,next;}e[MAXM];void add(int from,int to,int val){e[len].to=to;e[len].val=val;e[len].next=head[from];head[from]=len++;}void spfa(){int s=1;stack
    
      q;q.push(s);vis[s]=true;dis[s]=0;while(!q.empty()){int cur=q.top();q.pop();vis[cur]=false;for(int i=head[cur];i!=-1;i=e[i].next){int id=e[i].to;if(dis[id] > dis[cur] + e[i].val){dis[id]=dis[cur]+e[i].val;if(!vis[id]){q.push(id);vis[id]=true;}}}}}int main(){while(~scanf("%d%d",&n,&m)){for(int i=1;i<=n;i++){head[i]=-1;dis[i]=-INF;vis[i]=false;}len=0;for(int i=0;i