Apartments problem from CSES problem set

editorial
1

Why does my code give correct answer only for half the test cases?

#include<bits/stdc++.h>

using namespace std;

int main(){

int n,m;
unsigned long long k;
cin>>n>>m>>k;
vector<unsigned long long> desired(n);
for(int i=0;i<n;i++){
    cin>>desired[i];
}
vector<unsigned long long> available(m);
for(int i=0;i<m;i++){
    cin>>available[i];
}
int ans=0;
unordered_map<unsigned long long, int> mp;
for(int i=0;i<m;i++){
    mp[available[i]]++;
}
for(int i=0;i<n;i++){
    for(long long j =desired[i]-k ; j<= desired[i]+k ; j++ ){
        auto it = mp.find(j);
        if(it!=mp.end()){
            if(it->second!=0){
                ans++;
                it->second=(it->second)-1;
                break;
            }
        }
    }
}
cout<<ans<<endl;

return 0;

}

2

A simple implementation is here!

int solve(int n, int m, int k)
{
    int i=0,j=0,ans=0;
    vector<int> app(m,0),apt(n,0);

    for (auto &it : apt) cin >> it;
    sort(apt.begin(),apt.end()); 

    for (auto &it : app) cin >> it;
    sort(app.begin(),app.end()); 

    while(i<n and j<m)
    {
        if(abs(apt[i]-app[j]) <= k)
        {
            ans++;
            i++;
            j++;
        }
        else if(apt[i]<app[j])
            i++;
        else
            j++;
    }
    return ans;

}