Codeforces 620F Xors on Segments（暴力+DP）

 1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 #define rep(i, a, b)    for (int i(a); i <= (b); ++i)
 6 
 7 int x[1000010], a[50010], l[50010], r[50010], ans[5010];
 8 vector < pair <int, int> > v[50010];
 9 int n, q;
10 
11 int main(){
12 
13     rep(i, 1, 1000001) x[i] = x[i - 1] ^ i;
14     scanf("%d%d", &n, &q);
15     rep(i, 1, n) scanf("%d", a + i);
16     rep(i, 1, q){
17         scanf("%d%d", l + i, r + i);
18         v[r[i]].push_back({l[i], i});
19     }
20 
21     rep(i, 1, n){
22         int dp = 0;
23         rep(j, i, n){
24             dp = max(dp, x[a[i]] ^ x[a[j]] ^ min(a[i], a[j]));
25             for (auto u : v[j]){
26                 if (u.first <= i) ans[u.second] = max(ans[u.second], dp);
27             }
28         }
29     }
30 
31     rep(i, 1, q) printf("%d\n", ans[i]);
32     return 0;
33 }