dijkstra优化

const int N = 1e6+10;
int n, m;
struct _ {int to,w;};
vector<_> g[N];
int d[N];
queue<int> q[N];

void dij() {
	memset(d,0x3f,sizeof d);
	d[1] = 0, q[0].push(1);
	int mx = 0;
	REP(i,0,mx) while (q[i].size()) {
		int x = q[i].front(); q[i].pop();
		if (d[x]<i) continue;
		for (auto &&e:g[x]) {
			int dd = d[x]+e.w;
			if (dd<d[e.to]) { 
				d[e.to] = dd;
				if (dd>=N) continue;
				q[dd].push(e.to);
				mx = max(mx, dd);
			}
		}
	}
}