JOHNY: Getting WA when using std::find

help
1

I have to discuss the Problem whose CodeID is “JOHNY”
I didn’t got an AC from this problem until I gave up using std:find in my answer;
I replaced
cout<< ((std::find(A,A+K,Uncle_Johny[0])-A)+1) <<endl;
with
for (int i=0; i<N; i++) {
if (A[i]==Uncle_Johny[0]) {
//cout<<“ANS=”;
cout<<(i+1)<<endl;break;
}
}
and then got an AC.
But I’m still wondering why using std::find got me a Wrong Answer…
Should I post all my code on this place?

2

Yes please, and please either format it or (better!) link to your submission :slight_smile:

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3 
#include <iostream>
#include <algorithm>
using namespace std;
void CASE() {
    int N;
    int A[100];
    int Uncle_Johny[1];
    int K;
    cin>>N;
    for (int i=0; i<N; i++) {
        //A[i]=9999999;
        cin>> A[i];
    }
    cin>>K;
    Uncle_Johny[0]= A[K-1];
    sort(A,A+N);
    //cout<<"F=";
    //cout<< ((std::search(A,A+K,Uncle_Johny,Uncle_Johny+1)-A)+1) <<endl;  
    cout<< ((std::find(A,A+K,Uncle_Johny[0])-A)+1) <<endl;

    for (int i=0; i<N; i++) {
        if (A[i]==Uncle_Johny[0]) {
            //cout<<"ANS=";
            cout<<(i+1)<<endl;break;
        }
    }


}

int main()
{
    int T=(-1);
    cin>>T;
    for (int zz=0; zz<T; zz++) {
        CASE();
    }
    return 0;
}
1 Like
4

This code prints out two answers per testcase, so no wonder it’s getting WA :slight_smile:

Please post the code that only used std::find but got WA.

Edit:

One thing that leaps out is with:

cout<< ((std::find(A,A+K,Uncle_Johny[0])-A)+1) <<endl;

you are only searching through the first K elements of A, instead of all of A.

2 Likes
6

Thanks - see my Edit, above :slight_smile:

2 Likes
7 
#include <iostream>
#include <algorithm>
using namespace std;
void CASE() {
    int N;
    int A[100];
    int Uncle_Johny[1];
    int K;
    cin>>N;
    for (int i=0; i<N; i++) {
        //A[i]=9999999;
        cin>> A[i];
    }
    cin>>K;
    Uncle_Johny[0]= A[K-1];
    sort(A,A+N);
    //for (int i=0; i<N; i++) { cout<<"A:   "<<A[i]<<","; }
    //cout<<endl;
    //cout<<"F=";
    //cout<< ((std::search(A,A+K,Uncle_Johny,Uncle_Johny+1)-A)+1) <<endl;  //為什麼這個輸出是錯的??
    cout<< ((std::find(A,A+K,Uncle_Johny[0])-A)+1) <<endl;
/*
    for (int i=0; i<N; i++) {
        if (A[i]==Uncle_Johny[0]) {
            //cout<<"ANS=";
            cout<<(i+1)<<endl;break;
        }
    }
*/

}

int main()
{
    int T=(-1);
    cin>>T;
    for (int zz=0; zz<T; zz++) {
        CASE();
    }
    return 0;
}
8

I have got an AC by the following code

cout<< ((std::find(A,A+100,Uncle_Johny[0])-A)+1) <<endl;

But I am still wondering why…
In this problem, I put my data between A[0] and A[K-1].
There are only K elements mattering in this problem.
Why shall I search through all elements of this array?

9

Consider the testcase:

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