MnZn刚学OI，样例过了爆零，求助

#include <bits/stdc++.h>
using namespace std;
const int N = 2e6 + 5;
int val[N], cnt, size[N], pri[N], ls[N], rs[N], tag[N], n, q, rt;
inline int build(int w) {
    val[++cnt] = w;
    pri[cnt] = rand();
    size[cnt] = 1;
    return cnt;
}
inline void pushup(int p) {
    size[p] = size[ls[p]] + size[rs[p]] + 1;
}
inline void pushdown(int p) {
    if(!tag[p]) return;
    swap(ls[p], rs[p]);
    if(ls[p]) tag[ls[p]] ^= 1;
    if(rs[p]) tag[rs[p]] ^= 1;
    tag[p] = 0;
}
inline void split(int p, int siz, int &x, int &y) {
    if(!p) {
        x = y = 0;
        return;
    }
    pushdown(p);
    if(size[ls[p]] + 1 <= siz) {
        x = p;
        split(rs[p], siz - size[ls[p]] - 1, rs[p], y);
    } else {
        y = p;
        split(ls[p], siz, x, ls[p]);
    }
    pushup(p);
}
inline int merge(int x, int y) {
    if(!x || !y) return x + y;
    if(pri[x] > pri[y]) {
        pushdown(x);
        rs[x] = merge(rs[x], y);
        pushup(x);
        return x;
    } else {
        pushdown(y);
        ls[y] = merge(x, ls[y]);
        pushup(y);
        return y;
    }
}
inline void insert(int pos, int w) {
    int x, y;
    split(rt, pos - 1, x, y);
    rt = merge(merge(x, build(w)), y);
}
inline void flip(int l, int r) {
    int x, y, z;
    split(rt, l - 1, x, y);
    split(y, r, y, z);
    tag[y] ^= 1;
    rt = merge(merge(x, y), z);
}
inline void print(int p) {
    pushdown(p);
    if(ls[p]) print(ls[p]);
    printf("%d ", val[p]);
    if(rs[p]) print(rs[p]);
}
int main() {
    srand(time(NULL) * 1u);
    int l, r;
    scanf("%d%d", &n, &q);
    for(int i = 1; i <= n; i++) insert(i, i);
    for(int i = 1; i <= q; i++) {
        scanf("%d%d", &l, &r);
        flip(l, r);
    }
    print(rt);
    return 0;
}