PROG-1080: สามเหลี่ยมอีกครั้ง (triagain)

#include <bits/stdc++.h>

using namespace std;
const int INF = 2e9;
int ar[30010];
int n;

int BS(int ab, int l){
    int r = n, idx = -INF;
    while(l <= r){
        int mid = (l + r) / 2;
        if(ar[mid]< ab){
            idx = max(idx, mid);
            l = mid + 1;
        }
        else r = mid - 1;
    }
    return idx;
}

int main(){

    scanf("%d",&n);

    int prev = 0;
    for(int i = 1; i <= n; i++){
        scanf("%d", &ar[i]);
    }

    sort(ar + 1, ar + n + 1);

    int mx = 0;
    for(int i = 1; i <= n-2; i++){
        mx = max(mx, BS(ar[i] + ar[i+1], i+2) - i + 1);
    }

    if(mx == 0) printf("%d", n);
    else printf("%d", mx);

    return 0;
}