include <bits/stdc++.h>

using namespace std;

define int long long

define inf LLONG_MAX

define pb push_back

define deb cout<<"YES"<<endl

define fi first

define se second

define pii pair<int,int>

define lc 2*pos

define rc 2*pos+1

define fokus ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);

int calc(int n,int a){
    int x= 2*a + n-1; 
    x*=n; 
    x/=2;
    return x;

}

signed main(){ fokus vectorpul(10); pul[0]=1; for(int i=1;i<=6;i++) pul[i]=pul[i-1]*10; int t;cin>>t;while(t--){ int a,b,c,k;cin>>a>>b>>c>>k; if (a>b) swap(a,b); if (c-b!=1 && c-b!=0){ cout<<-1<<endl; continue; } int l=pul[a-1],r=pul[a]-1; bool yes=0; while(l<=r){ int mid=(l+r)/2; int aa=pul[b]-1-max(pul[c-1]-pul[a-1],1ll)+1; int cc=max(0ll,pul[b]-1+pul[a-1]-(pul[c]-1)); aa-=cc; int prev=calc(mid-1-pul[a-1]+1,aa); int cur=calc(mid-pul[a-1]+1,aa); // cout<<mid<<" "<<prev<<" "<<cur<<" "<<aa<<endl; int dif=k-prev; int tar=max(pul[c-1]-mid-1,0ll)+dif; int mi=tar+mid; if (prev<=k && k<=cur && mi<=pul[c]){ cout<<mid<<" + "<<tar<<" = "<<mi<<endl; yes=1; break; } else if (cur<k) l=mid+1; else r=mid-1; } if (!yes) cout<<-1<<endl;

}

} Hi! So this is the problem: https://codeforces.net/contest/1836/problem/C I think the solution is basically the same but I am using binary search (which is actually not needed but yeah the idea should have been the same) but this is incorrect... does anyone know where is the fault or is it logic fault? thank you so much!