P5459 [BJOI2016]回转寿司

P5459 [BJOI2016]回转寿司

求多少个 $l, r$ 满足 $L\le s _r - s _ l \le R$ 。

查看代码

#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long LL;
const int N = 1e5 + 10;
int n, L, R;
LL ans, s[N];
void cdq(int l, int r)
{
    if (l == r)
        return;
    int mid = l + r >> 1;
    cdq(l, mid);
    cdq(mid + 1, r);
    int hd = l, tl = l - 1;
    for (int i = mid + 1; i <= r; i++)
    {
        while (tl + 1 <= mid && s[i] - s[tl + 1] >= L)
            tl++;
        while (hd <= mid && s[i] - s[hd] >= R)
            hd++;
        ans += tl - hd + 1;
    }
    sort(s + l, s + r + 1);
}
int main()
{
    scanf("%d%d%d", &n, &L, &R);
    for (int i = 1; i <= n; i++)
    {
        scanf("%lld", &s[i]);
        s[i] += s[i - 1];
    }
    cdq(0, n);
    printf("%lld", ans);
    return 0;
}