nhanh giúp em nhé ạ

làm bằng c++ ạ

#include<bits/stdc++.h>
#define ll long long
using namespace std;

int main() {
    ll n,k;
    cin >> n;
    vector<int> a(n);
    for (int i=0; i<n; ++i) {
        cin >>a[i];
    }
    cin>>k;
    //meothinhle
    auto s=upper_bound(a.begin(),a.end(),k);
    if (s!=a.begin()) cout<<*(--s);
    return 0;
}

#include <iostream>
#include <vector>
using namespace std;
int f(const vector<int>& a, int k){
    int l=0,r=a.size()-1;
    while(l<=r){
        int m=l+(r-l)/2;
        if(a[m]<=k) l=m+1;
        else r=m-1;
    }
    return r;
}
int main(){
    int n,k;
    cin>>n;
    vector<int> a(n);
    for(int i=0;i<n;++i) cin>>a[i];
    cin>>k;
    int res=f(a,k);
    if(res>=0&&a[res]<=k) cout<<a[res]<<endl;
    else cout<<"khong"<<endl;
    return 0;
}