【关键路径】hdu 4109

#include <map>
#include <set>
#include <list>
#include <queue>
#include <deque>
#include <stack>
#include <string>
#include <time.h>
#include <cstdio>
#include <math.h>
#include <iomanip>
#include <cstdlib>
#include <limits.h>
#include <string.h>
#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;

#define LL long long
#define MIN INT_MIN
#define MAX INT_MAX
#define PI acos(-1.0)
#define FRE freopen("input.txt","r",stdin)
#define FF freopen("output.txt","w",stdout)
#define N 1005
struct node{
    int y,w;
};
vector<node> v[N];
int n,m;
int tt[N];
int in[N];
void init () {
    int i;
    for (i = 0; i <= n; i++ ) v[i].clear();
}
void gao () {
    int i,j;
    queue<int> qq;
    for (i = 0 ; i < n ; i++) {
        tt[i] = 0;
        if (!in[i]) {
            qq.push(i);
            tt[i] = 1;
        }
    }
    while (!qq.empty()) {
        int x = qq.front();
        qq.pop();
        for (i = 0; i < v[x].size(); i++) {
            node tmp = v[x][i];
            int y = tmp.y;
            tt[y] = max(tt[y],tt[x] + tmp.w);
            in[y]--;
            if (!in[y]) {
                qq.push(y);
            }
        }
    }
    int ans = 0;
    for (i = 0; i < n; i++) {
        ans = max(ans,tt[i]);
    }
    printf("%d\n",ans);
}
int main () {
   while (scanf("%d%d",&n,&m) != EOF)  {
       int i,j;
       init();
       memset(in,0,sizeof(in));
       for (i = 0; i < m; i++) {
           int a,b,c;
           scanf("%d%d%d",&a,&b,&c);
           in[b]++;
           node tmp;
           tmp.y = b;
           tmp.w = c;
           v[a].push_back(tmp);
       }
       gao();
   }
   return 0;
}