rt，完全没看懂它要干什么

贴代码：

#include <iostream>
#include <vector>
#include <queue>
using namespace std;
const int MAXN = 200001;
int main() {
	int n, m, l, r, w;
	cin >> n >> m;
	vector <int> dist(MAXN, -1);
	vector <bool> vis(MAXN, false);
	vector <vector <pair<int, int> > > go(MAXN);
	for(int i = 1; i <= m; i++) {
		cin >> l >> r >> w;
		go[l].push_back(make_pair(r + 1, w));
		go[r + 1].push_back(make_pair(l, -w));
	}
	queue <int> q;
	dist[1] = 0, vis[1] = true;
	q.push(1);
	while(!q.empty()) {
		int x = q.front(); q.pop();
		for(auto i : go[x]) {
			if(!vis[i.first]) {
				vis[i.first] = true;
				dist[i.first] = dist[x] + i.second;
				q.push(i.first);
			}
		}
	}
	if(dist[n + 1] == -1) cout << "sorry" << endl;
	else cout << dist[n + 1] << endl;
	return 0;
}