Leetcode-743 Network Delay Time(网络延迟时间)

#define INF 0x3f3f3f3f
const int maxn = 503;
#define _for(i,a,b) for(int i = (a);i < (b);i ++)
struct edge
{
    int to;
    int cost;
};

//G[s].push_back(t);from s to t,directed

class Solution
{
    public:
        int d[maxn];
        int V,E;
        vector<edge> G[maxn];
    //from s to other V
        void shortest_path(int s)
        {
            _for(i,0,V)
            d[i] = INF;

            d[s] = 0;
            while(1)
            {
                bool update = false;
                _for(i,0,V)
                {
                    _for(j,0,G[i].size())
                    {
                        edge e = G[i][j];
                        if(d[i] != INF && d[e.to] > d[i] + e.cost)
                        {
                            d[e.to] = d[i] + e.cost;
                            update = true;
                        }
                    }
                }
                if(!update) break;
            }
        }
        int networkDelayTime(vector<vector<int>>& times, int N, int K)
        {
            V = N;
            _for(i,0,times.size())
            {
                G[times[i][0]-1].push_back(edge{times[i][1]-1,times[i][2]});
                E ++;
            }
            
            shortest_path(K-1);
          //  cout << d[1] << endl;
            int cnt = 0;
            _for(i,0,V)
            {
                if(d[i]==INF)   return -1;
                cnt = max(cnt,d[i]);
            }
            return cnt;
        }
};