RT,MaxN设成1e5会RE，但设成1e6就过了(第三行)

#include<bits/stdc++.h>
#define ll long long
#define MaxN 1114514
#define lc (p << 1)
#define rc ((p << 1) | 1)
#define mid ((l + r) >> 1)

using namespace std;

int dc[MaxN << 1]; //discreate

struct ScanLine {
	ll l, r, h;
	int k;
	bool operator < (const ScanLine &rhs) const {
		return h < rhs.h;
	}
} a[MaxN << 1];

struct SegTree {
    ll len, cnt;
} tr[MaxN << 2];

void build(int p, int l, int r) {
    //cout << l << " " << r << endl;
    if(l == r) {
    	tr[p].len = 0, tr[p].cnt = 0;
        return;
    }
    build(lc, l, mid);
    build(rc, mid + 1, r);
}

void pushup(int p, int l, int r) {
    if(tr[p].cnt > 0) {
        tr[p].len = dc[r + 1] - dc[l];
    } else {
        tr[p].len = tr[lc].len + tr[rc].len;
    }
}

void update(int p, ll l, ll r, int s, int t, int k) {
    if(l >= dc[t + 1] || r <= dc[s]) return;

    if(l <= dc[s] && dc[t + 1] <= r) {
        tr[p].cnt += k;
//        tr[p].len = dc[t + 1] - dc[s];
        pushup(p, s, t);
        return;
    }

    if(l <= dc[s + t >> 1]) update(lc, l, r, s, s + t >> 1, k);
    if(dc[(s + t >> 1) + 1] <= r) update(rc, l, r, (s + t >> 1) + 1, t, k);
    pushup(p, s, t);
}

int main(){
    //freopen("owo.txt", "w", stdout);

	int n;
	scanf("%d", &n);
	for(int i = 1; i <= n; i++) {
		ll _x1, _y1, _x2, _y2;
		scanf("%lld%lld%lld%lld", &_x1, &_y1, &_x2, &_y2);

		int t = (i << 1) - 1;
		dc[t] = _x1, dc[t + 1] = _x2;
        a[t] = (ScanLine){_x1, _x2, _y1, 1};
        a[t + 1] = (ScanLine){_x1, _x2, _y2, -1};
	}

	n <<= 1;
	sort(a + 1, a + n + 1);
	sort(dc + 1, dc + n + 1);
	int m = unique(dc + 1, dc + n + 1) - (dc + 1);

    ll ans = 0;
	build(1, 1, m - 1);
	for(int i = 1; i < n; i++) {
        update(1, a[i].l, a[i].r, 1, m - 1, a[i].k);
        ans += tr[1].len * (a[i + 1].h - a[i].h);
//        cout << tr[1].len  << " " << a[i + 1].h - a[i].h << endl;
	}
	printf("%lld", ans);
	return 0;
}