裸的cdq， 沒啥好說的， 要註意mid左邊和mid右邊的a相同的情況。

#include<bits/stdc++.h>
#define LL long long
#define fi first
#define se second
#define mk make_pair
#define PLL pair<LL, LL>
#define PLI pair<LL, int>
#define PII pair<int, int>
#define SZ(x) ((int)x.size())
#define ull unsigned long long
using
 
 namespace std;

const int N = 5e5 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + 7;
const double eps = 1e-8;

int n;

struct node {
    int a, b, c;
    bool die;
} p[N], tmp[N];

bool cmpa(const node& x, const node& y) {
    return x.a > y.a;
}
 
bool cmpb(const node& x, const node& y) {
    return x.b > y.b;
}

void cdq(int l, int r) {
    if(l == r) return;
    int mid = l + r >> 1;
    int v1 = p[mid].a, v2 = p[mid + 1].a;
    cdq(l, mid); cdq(mid + 1, r);
    int mx = 0, mx2 = 0;
    for(int i = mid + 1, j = l; i <= r; i++) {
        
 
while(j <= mid && p[j].b > p[i].b) {
            mx = max(mx, p[j].c);
            if(p[j].a > v1) mx2 = max(mx2, p[j].c);
            j++;
        }
        if(p[i].a == v1) {
            if(mx2 > p[i].c) p[i].die = true;
        } else {
            if(mx > p[i].c) p[i].die = true;
        }
    }
    int p1 = l, p2 = mid + 1, tot = l;
    while(p1 <= mid && p2 <= r)
        if(p[p1].b >= p[p2].b) tmp[tot++] = p[p1], p1++;
        else tmp[tot++] = p[p2], p2++;
    while(p1 <= mid) tmp[tot++] = p[p1], p1++;
    while(p2 <= r) tmp[tot++] = p[p2], p2++;
    for(int i = l; i <= r; i++) p[i] = tmp[i];
}

int main() {
    scanf("%d", &n);
    for(int i = 1; i <= n; i++) scanf("%d", &p[i].a);
    for(int i = 1; i <= n; i++) scanf("%d", &p[i].b);
    for(int i = 1; i <= n; i++) scanf("%d", &p[i].c);
    int cnt = 0;
    sort(p + 1, p + 1 + n, cmpa);
    cdq(1, n);
    for(int i = 1; i <= n; i++) if(p[i].die) cnt++;
    printf("%d\n", cnt);
    return 0;
}

/*
*/

Codeforces 12D Ball cdq分治