题目

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;
const int N = sqrt(1e9) + 1;const int mod = 1e9 + 7;
// const int mod = 998244353;
//const __int128 mod = 212370440130137957LL;
// int a[505][5005];
// bool vis[505][505];int a[maxn], b[maxn];
bool vis[maxn];
string s[maxn];
int n, m;struct Node{int val, id;bool operator<(const Node &u)const{return val < u.val;}
};
// Node c[maxn];
int ans[maxn];
int sum[maxn];
int Xor[maxn];int f[20][10][10];
//long long ? maxn ? n? m?void solve(){int res = 0;int q, k;int x;cin >> n >> q;// for(int i = 1; i <= n; i++){//     cin >> a[i];// }for(int i = 1; i <= n; i++){cin >> a[i];sum[i] = sum[i - 1] + a[i];Xor[i] = Xor[i - 1] ^ a[i];}map<int, vector<int>> mp[2];for(int i = 1; i <= n; i++){mp[i % 2][Xor[i]].pb(i);}auto ask = [&](int l, int r){if(sum[r] == sum[l - 1]) return 0;if(Xor[r] != Xor[l - 1]) return -1;if((r - l + 1) % 2 == 1) return 1;if(a[l] == 0 || a[r] == 0) return 1;vector<int> &vec = mp[l % 2][Xor[l - 1]];//不加&就超时！！！！！！！auto it = lower_bound(vec.begin(), vec.end(), l);if(it == vec.end()) return -1;int pos = *it;if(pos <= r) return 2;return -1;};while(q--){int l, r;cin >> l >> r;cout << ask(l, r) << '\n';}
}   signed main(){ios::sync_with_stdio(0);cin.tie(0);int T = 1;// cin >> T;while (T--){solve();}return 0;
}