Laptop (thinking, two-dimensional partial order)

Laptop

The meaning of the title: n items, each item has two attributes $a_i,b_i$, Ask how many items j, satisfy $\exists$ Article$i(i\ne j)$使$a_i\ge a_j,b_i\ge b_j$

Idea: First sort one of the attributes a from large to small, then enumerate each item, and set a maximum value $mx\; is$ used to storebbduring enumerationThe maximum value of$b$ , if the current item’s$b\; is$ less than$mx$， years ++。

Simple proof: in the enumeration process, $a_i\ge a_{i+1}$. So, $mx$ is the maximum value among the first i items, if$i>j，b_j<mx$ , it means that j is an item that meets the conditions.

$Code$

#include<bits/stdc++.h>
using namespace std;
struct f {
    
    
    long long a, b;
} s[100010];
bool cmp(f x, f y) {
    
    
   return x.a > y.a;
}
int main() {
    
    
    int n;
    cin >> n;
    for(int i=0; i<n; i++) {
    
    
        cin >> s[i].a >> s[i].b;
    }
    sort(s, s+n, cmp);

    int mx = s[0].b, ans = 0;
    for(int i=1; i<n; i++) {
    
    
        if(s[i].b <= mx) ans++;
        else mx = s[i].b;
    }
    cout << ans;
    return 0;
}