思路:
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define fi first
#define se second
#define lson p << 1
#define rson p << 1 | 1
const int maxn = 1e6 + 5, inf = 1e18, maxm = 4e4 + 5, base = 37;
const int N = 1e6;
const int mod = 1e9 + 7;
// const int mod = 998244353;
//const __int128 mod = 212370440130137957LL;
// int a[1005][1005];
// bool vis[505][505];
// char s[2005][2005];
int n, m;
int a[maxn];
// string s;
struct Node{
// int val, id;
// bool