这份代码：

#include<bits/stdc++.h>
using namespace std;
const int N = 1e5 + 9,SqrtN = 502;
int n,m;
int a[N];
struct node{
    int num,id;
} tmp[N];
bool cmp(node x,node y){
    return x.num < y.num;
}
struct block{
	int l,r;
} b[SqrtN];
int block_len,block_cnt;
int belong[N];
void build_block(){
	block_len = 300;block_cnt = (n + block_len - 1) / block_len;
	for(int i = 1;i <= block_cnt;i++){
		b[i].l = b[i - 1].r + 1;
		b[i].r = b[i].l + block_len - 1;
	}
	b[block_cnt].r = n;
	for(int i = 1;i <= block_cnt;i++)
		for(int j = b[i].l;j <= b[i].r;j++)
			belong[j] = i;
}

struct BinaryIndexedTree{
	int BIT[N];
	int lowbit(int x){
		return x & (-x);
	}
	void update(int pos,int v){
		for(int i = pos;i <= n;i += lowbit(i))
			BIT[i] += v;
	}
	int query(int pos){
		int ret = 0;
		for(int i = pos;i;i -= lowbit(i))
			ret += BIT[i];
		return ret;
	}
} bit;

int L[N];//L[i]：[b[belong[i]].l,i]这一段的逆序对数 
int R[N];//R[i]：[i,b[belong[i]].r]这一段的逆序对数
int ans[SqrtN][SqrtN];//ans[i][j]：第i到j块之间的逆序对数 
int cnt[SqrtN][N]; //cnt[i][j]：前i块中小于等于j的数的个数 

int tmp1[SqrtN],top1;
int tmp2[SqrtN],top2;

void init(){
	//块内排序 
	for(int i = 1;i <= block_cnt;i++)
		sort(tmp + b[i].l,tmp + b[i].r + 1,cmp);

	//预处理L和R
	for(int i = 1;i <= block_cnt;i++){
        int temp = 0;
		for(int j = b[i].l;j <= b[i].r;j++){
			bit.update(a[j],1);
			temp += bit.query(n) - bit.query(a[j]);
            L[j] = temp;
		}
		for(int j = b[i].l;j <= b[i].r;j++)
			bit.update(a[j],-1);
	}

	for(int i = 1;i <= block_cnt;i++){
        int temp = 0;
		for(int j = b[i].r;j >= b[i].l;j--){
			bit.update(a[j],1);
			temp += bit.query(a[j] - 1);
            R[j] = temp;
		}
		for(int j = b[i].l;j <= b[i].r;j++)
			bit.update(a[j],-1);
	}

	//预处理ans
	for(int i = 1;i <= block_cnt;i++)
		for(int j = i;j <= block_cnt;j++){
            if(i == j){
                ans[i][j] = L[b[i].r];
                continue;
            }
			int pos1 = b[i].l,pos2 = b[j].l,temp = 0;
			while(pos1 <= b[i].r && pos2 <= b[j].r){
				if(pos2 > b[j].r || tmp[pos1].num < tmp[pos2].num)
					pos1++;
				else{
					temp += b[i].r - pos1 + 1;
					pos2++;
				}
			}
			ans[i][j] = ans[i + 1][j] + ans[i][j - 1] - ans[i + 1][j - 1] + temp; 
		}

	//预处理cnt
	for(short i = 1;i <= block_cnt;i++){
		for(int j = b[i].l;j <= b[i].r;j++)
			cnt[i][a[j]] = 1;
		for(int j = 1;j <= n;j++)
			cnt[i][j] = cnt[i][j] + cnt[i][j - 1] + cnt[i - 1][j] - cnt[i - 1][j - 1];
	}
}
long long query(int l,int r){
	int pos_l = belong[l],pos_r = belong[r];
	long long ret = 0;
	cout << "DEBUG\n";
	if(pos_l == pos_r){
		ret = L[r] - L[l - 1];
        top1 = 0;top2 = 0;
        for(int i = b[pos_l].l;i <= b[pos_l].r;i++){
            if(tmp[i].id <= l - 1)
                tmp1[++top1] = tmp[i].num;
            if(l <= tmp[i].id && tmp[i].id <= r)
                tmp2[++top2] = tmp[i].num;
        }
		int pos1 = 1,pos2 = 1,temp = 0;
		while(pos1 <= top1 && pos2 <= top2){
			if(pos2 > top2 || tmp1[pos1] < tmp2[pos2])
				pos1++;
			else{
				temp += top1 - pos1 + 1;
				pos2++;
			}
		}
		ret -= temp;
		return ret;
	}
	cout << "DEBUG0\n";
	ret = ans[pos_l + 1][pos_r - 1] + R[l] + L[r];
    top1 = 0;top2 = 0;
    for(int i = b[pos_l].l;i <= b[pos_l].r;i++)
        if(tmp[i].id >= l)
            tmp1[++top1] = tmp[i].num;
    for(int i = b[pos_r].l;i <= b[pos_r].r;i++)
        if(tmp[i].id <= r)
            tmp2[++top2] = tmp[i].num;
	cout << "DEBUG1\n";
	int pos1 = 1,pos2 = 1,temp = 0;
	while(pos1 <= top1 && pos2 <= top2){
		if(pos2 > top2 || tmp1[pos1] < tmp2[pos2])
			pos1++;
		else{
			temp += top1 - pos1 + 1;
			pos2++;
		}
	}
	cout << "DEBUG2\n";
	for(int i = l;i <= b[pos_l].r;i++)
		ret += cnt[pos_r - 1][a[i] - 1] - cnt[pos_l][a[i] - 1];
	cout << "DEBUG3\n";
	for(int i = b[pos_r].l;i <= r;i++)
		ret += (cnt[pos_r - 1][n] - cnt[pos_l][n]) - (cnt[pos_r - 1][a[i]] - cnt[pos_l][a[i]]);
	cout << "DEBUG4\n";
	return ret;
}
int main(){
	freopen("P5046.in","r",stdin);
	freopen("P5046.out","w",stdout);
	//ios::sync_with_stdio(false);
	//cin.tie(0);cout.tie(0);
	cin >> n >> m;
	build_block();
	for(int i = 1;i <= n;i++){
		cin >> a[i];
		tmp[i] = (node){a[i],i};
	}
	init();
	long long ans = 0;
	int l = 0,r = 0;
	while(m--){
		cout << "debug0\n";
		cout << l << ' ' << r << '\n';
		cin >> l >> r;
		cout << l << ' ' << r << '\n';
		cout << "debug\n";
		l ^= ans;r ^= ans;
		cout << "debug1\n";
		cout << l << ' ' << r << '\n';
		ans = query(l,r);
		cout << ans << '\n';
		cout << "qwq\n";
	}
	return 0;
}

我通过调试发现 bug 出在 cin >> l >> r 这里，但始终不知道为什么。