rt, $\mathcal{O}(nm \log m)$ 最慢点115ms

#include <iostream>
#include <vector>
#include <tuple>
#include <algorithm>
using namespace std;
const int maxn = 1e6 + 10;
int n, m;
bool c[maxn];
vector<tuple<int, int, int> > g, v;
void update(int l, int r, bool v) {for (int i = l; i <= r; i++) c[i] = v;}
int query(int l, int r) {
    int res = 0; for (int i = l; i <= r; i++) res += c[i];
    return res;
}
bool check(int x) {
    v.clear(); for (int i = 0; i <= x; i++) v.push_back(g[i]);
    sort(v.begin(), v.end()); reverse(v.begin(), v.end()); update(1, n, 0);
    auto [p, L, R] = v[0]; int l = L, r = R;
    for (int i = 1; i <= x; i++) {
        auto [P, cl, cr] = v[i];
        if (p == P) {
            L = min(L, cl); R = max(R, cr);
            l = max(l, cl); r = min(r, cr);
            if (l > r) return true;
        } else {
            if (query(l, r) == r - l + 1) return true;
            update(L, R, 1);
            p = P; l = L = cl; r = R = cr;
        }
    }
    return query(l, r) == r - l + 1;
}
int main() {
    ios::sync_with_stdio(false);
    cin >> n >> m; g.resize(m);
    for (auto& [x, l, r] : g) cin >> l >> r >> x;
    int l = 1, r = g.size() - 1, res = -1;
    while (l <= r) {
        int mid = (l + r) >> 1;
        if (check(mid)) r = mid - 1, res = mid;
        else l = mid + 1;
    } cout << res + 1 << '\n';
    return 0;
}