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  • codeforces 665E E. Beautiful Subarrays(trie树)

    题目链接:

    E. Beautiful Subarrays

    time limit per test
    3 seconds
    memory limit per test
    512 megabytes
    input
    standard input
    output
    standard output

    One day, ZS the Coder wrote down an array of integers a with elements a1,  a2,  ...,  an.

    A subarray of the array a is a sequence al,  al  +  1,  ...,  ar for some integers (l,  r) such that 1  ≤  l  ≤  r  ≤  n. ZS the Coder thinks that a subarray of a is beautiful if the bitwise xor of all the elements in the subarray is at least k.

    Help ZS the Coder find the number of beautiful subarrays of a!

    Input
     

    The first line contains two integers n and k (1 ≤ n ≤ 106, 1 ≤ k ≤ 109) — the number of elements in the array a and the value of the parameter k.

    The second line contains n integers ai (0 ≤ ai ≤ 109) — the elements of the array a.

    Output
     

    Print the only integer c — the number of beautiful subarrays of the array a.

    Examples
     
    input
    3 1
    1 2 3
    output
    5
    input
    3 2
    1 2 3
    output
    3
    input
    3 3
    1 2 3
    output
    2


    题意

    给n个数,问有多少对数满足a[i]^a[i+1]^...^a[j]>=k;

    思路

    处理出前缀异或和,再用trie树搞;

    AC代码

    #include <bits/stdc++.h>
    using namespace std;
    #define Riep(n) for(int i=1;i<=n;i++)
    #define Riop(n) for(int i=0;i<n;i++)
    #define Rjep(n) for(int j=1;j<=n;j++)
    #define Rjop(n) for(int j=0;j<n;j++)
    #define mst(ss,b) memset(ss,b,sizeof(b));
    typedef long long LL;
    const LL mod=1e9+7;
    const double PI=acos(-1.0);
    const int inf=0x3f3f3f3f;
    const int N=2e7+6;
    int n,k,cnt=2;
    int tree[N][2],val[N];
    void add_num(int num)
    {
        int x=1;
        for(int i=30;i>=0;i--)
        {
            int y=(num>>i)&1;
            if(!tree[x][y])tree[x][y]=cnt++;
            val[x]++;
            x=tree[x][y];
        }
        val[x]++;
    }
    LL get_ans(int num,int fy)
    {
        LL sum=0;
        int x=1;
        for(int i=30;i>=0;i--)
        {
            int y=(fy>>i)&1;
            int fx=(num>>i)&1^1;
            if(y==0)
            {
                sum+=(LL)val[tree[x][fx]];
                x=tree[x][fx^1];
            }
            else x=tree[x][fx];
        }
        return sum+(LL)val[x];
    }
    int main()
    {
        scanf("%d%d",&n,&k);
        int pre=0;
        LL ans=0;
        add_num(0);
        Riep(n)
        {
            int a;
            scanf("%d",&a);
            pre^=a;
            ans+=(LL)get_ans(pre,k);
            add_num(pre);
        }
        printf("%I64d
    ",ans);
    
        return 0;
    }


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  • 原文地址:https://www.cnblogs.com/zhangchengc919/p/5456980.html
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