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-;

const int mod = 1e9+;

const int inf = ;

const int dir[][] = { {-, }, {, }, {, -}, {, } };

int a[], ans[], b[], dp[];

struct node

{

    int l, r;

}q[];

int main()

{

    int n, m;

    cin>>n>>m;

    for(int i = ; i<=n; i++) {

        scanf("%d", &a[i]);

    }

    for(int i = ; i<=; i++) {

        b[i] = i^b[i-];

    }

    for(int i = ; i<m; i++) {

        scanf("%d%d", &q[i].l, &q[i].r);

    }

    for(int i = ; i<=n; i++) {

        dp[i] = a[i];

        for(int j = i+; j<=n; j++) {

            int minn = min(a[i], a[j]);

            int maxx = max(a[i], a[j]);

            int num = b[maxx]^b[minn-];

            dp[j] = max(dp[j-], num);

        }

        for(int j = ; j<m; j++) {

            if(i>=q[j].l&&i<=q[j].r) {

                ans[j] = max(ans[j], dp[q[j].r]);

            }

        }

    }

    for(int i = ; i<m; i++)

        printf("%d\n", ans[i]);

    return ;

}