Need help in the problem : https://www.codechef.com/AGPR2020/problems/ALPR2002

help
1

Hi i need help to solve this problem.

2

Anyone please suggest me the approach to sole this

3

Sort the sets, if y2 -y1 / x2 - x1 is constant then 2 else 0.

4

static boolean check_slope(long x1,long y1,long x2,long y2,long x3,long y3)
{
if( ((y2-y1)(x3-x2)) == ((y3-y2)(x2-x1)))
return true;
return false;
}
static boolean is_valid(int x[],int y[],int n)
{

for(int i=1;i<(n-1);i++)
if(!check_slope(x[i-1],y[i-1],x[i],y[i],x[i+1],y[i+1]))
return false;

 return true;

}

5

I was doing this during contest . X and Y are sorted and checking for the equality of slopes between 3 consecutive points. I is_valid is true then ans is 2 otherwise ans will be 0 .Could you please tell me what is wrong in this

6

I don’t think long int is large enough to store 10^18

7

Could you please share link of your solution

8

Ok maybe I’m a bit wrong. You’ll have to check both forward and backward seperately.

#include <iostream>
#include <bits/stdc++.h>
#include <cmath>
#include <vector>
#define ll long long int
#define mp make_pair
#define pb push_back
#define vi vector<int>
using namespace std;
using namespace std::chrono;
long long int p=1e9 +7;
ll solve(){
  int n;
  cin>>n;
  ll x[n];
  ll y[n];
  for(int i=0;i<n;i++){
      cin>>x[i];
  }
  for(int i=0;i<n;i++){
      cin>>y[i];
  }
  int ans=2;
  sort(x,x+n);
  sort(y,y+n);
  ll ydiff=y[1]-y[0];
  ll xdiff=x[1]-x[0];
  for(int i=2;i<n;i++){
      if( (y[i]-y[i-1])*xdiff != (x[i]-x[i-1])*ydiff ){
          ans--;
          break;
      }
  }
  sort(y,y+n,greater<int>());
  ydiff=y[1]-y[0];
  for(int i=2;i<n;i++){
      if( (y[i]-y[i-1])*xdiff != (x[i]-x[i-1])*ydiff ){
          ans--;
          break;
      }
  }
  return ans;
}
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
	int t;
	cin >>t;
	//t=1;
    srand(time(0));
	while(t--){
	       cout<<solve()<<"\n";
	}
}
9

Got it , thanks .