codeforces 620F. Xors on Segments

题目链接

定义一种操作f(u, v) = u^u+1^.......^v。 (u<=v)， 给n个数， q个询问， 每个询问给出一个区间[l, r]， 求这个区间里的f(a[i], a[j]) (l<=i<=j<=r)的最大值。

一开始竟然用n^2m的方法， 真是有点脑残..

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <queue>
#include <stack>
#include <bitset>
using namespace std;
#define pb(x) push_back(x)
#define ll long long
#define mk(x, y) make_pair(x, y)
#define lson l, m, rt<<1
#define mem(a) memset(a, 0, sizeof(a))
#define rson m+1, r, rt<<1|1
#define mem1(a) memset(a, -1, sizeof(a))
#define mem2(a) memset(a, 0x3f, sizeof(a))
#define rep(i, n, a) for(int i = a; i<n; i++)
#define fi first
#define se second
typedef pair<int, int> pll;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int mod = 1e9+7;
const int inf = 1061109567;
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
int a[50005], ans[5005], b[1000005], dp[50005];
struct node
{
    int l, r;
}q[5005];
int main()
{
    int n, m;
    cin>>n>>m;
    for(int i = 1; i<=n; i++) {
        scanf("%d", &a[i]);
    }
    for(int i = 1; i<=1000000; i++) {
        b[i] = i^b[i-1];
    }
    for(int i = 0; i<m; i++) {
        scanf("%d%d", &q[i].l, &q[i].r);
    }
    for(int i = 1; i<=n; i++) {
        dp[i] = a[i];
        for(int j = i+1; j<=n; j++) {
            int minn = min(a[i], a[j]);
            int maxx = max(a[i], a[j]);
            int num = b[maxx]^b[minn-1];
            dp[j] = max(dp[j-1], num);
        }
        for(int j = 0; j<m; j++) {
            if(i>=q[j].l&&i<=q[j].r) {
                ans[j] = max(ans[j], dp[q[j].r]);
            }
        }
    }
    for(int i = 0; i<m; i++)
        printf("%d\n", ans[i]);
    return 0;
}