[POJ1201]Intervals（差分约束）

题目描述

传送门

题解

和上一道题基本一样：POJ1716

代码

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

const int max_N=5e4+5;
const int max_m=max_N*2;
const int max_e=max_m*2;
const int INF=1e9;

int n,N,M,l,r,w,u,t,ans;
int tot,point[max_N],next[max_e],v[max_e],c[max_e];
int dis[max_N];
bool vis[max_N];
queue <int> q;

inline void addedge(int x,int y,int z){
    ++tot; next[tot]=point[x]; point[x]=tot; v[tot]=y; c[tot]=z;
}

inline void spfa(){
    memset(dis,128,sizeof(dis));
    memset(vis,0,sizeof(vis));
    dis[0]=0;
    vis[0]=true;
    while (!q.empty()) q.pop();
    q.push(0);

    while (!q.empty()){
        int now=q.front(); q.pop();
        vis[now]=false;
        for (int i=point[now];i;i=next[i])
          if (dis[v[i]]<dis[now]+c[i]){
            dis[v[i]]=dis[now]+c[i];
            if (!vis[v[i]]){
                vis[v[i]]=true;
                q.push(v[i]);
            }
          }
    }
}

int main(){
    scanf("%d",&n);
    N=0;
    for (int i=1;i<=n;++i){
        scanf("%d%d%d",&l,&r,&w);
        u=l;
        t=r+1;
        N=max(N,t);
        addedge(u,t,w);
    }
    for (int i=0;i<N;++i){
        addedge(i+1,i,-1);
        addedge(i,i+1,0);
    }

    spfa();

    ans=dis[N];
    printf("%d\n",ans);
}