【luogu P4462 [CQOI2018]异或序列】 题解

题目链接：https://www.luogu.org/problemnew/show/P4462

a_x+a_x-1+...+a_y = cnt_x+cnt_{y 这样把一段序列变成两段相加跑莫队。}

#include <cstdio>
#include <algorithm>
#include <iostream>
#include <cmath>
using namespace std;
const int maxn = 200010;
int curR = 0, curL = 1, answer,a[maxn], ans[maxn], cnt[maxn], n, m, k, bl;
struct query{
    int l,r,p;
}q[maxn];

bool cmp(const query &a, const query &b)
{
    return (a.l/bl) == (b.l/bl) ? a.r<b.r : a.l<b.l;
}

inline void add(int pos)
{
    cnt[a[pos]]++;
    answer+=cnt[a[pos]^k];
}

inline void remove(int pos)
{
    cnt[a[pos]]--;
    answer-=cnt[a[pos]^k];
}

int main()
{
    scanf("%d%d%d",&n,&m,&k);
    bl = sqrt(n);
    cnt[0] = 1;
    for(int i = 1; i <= n; i++)
    {
        scanf("%d",&a[i]);
        a[i] ^= a[i-1]; 
    }
    
    for(int i = 1; i <= m; i++)
    {
        scanf("%d%d",&q[i].l,&q[i].r);
        q[i].p = i;
    }
    
    sort(q+1,q+1+m,cmp);
    
    for(int i = 1; i <= m; i++)
    {
        while(curL < q[i].l) remove(curL-1),curL++;
        while(curL > q[i].l) curL--,add(curL-1);
        while(curR < q[i].r) add(++curR);
        while(curR > q[i].r) remove(curR--);
        ans[q[i].p] = answer;
    }
    for(int i = 1; i <= m; i++)
    printf("%d
",ans[i]);
    return 0;
}