/*  Matching Numbers (15 points)

Write a complete C program that asks the user to enter a number N in the 
range 1 to 20 (inclusive). If the user enters a number outside this range the 
program must ask the user to enter the number again. The program must then 
generate two sets of N random numbers, where each number is in the 
range [0,..,9], print the two sets on the screen (one set per line),
and then print the numbers that appear in both sets, if any.
Format the output similar to the sample runs shown below.

SAMPLE RUN #1:
==============

Please enter N in the range [1,20]: 7

First set:   0, 5, 2, 5, 2, 6, 8,
Second set:  3, 1, 8, 9, 3, 5, 3,

The following numbers appear in both sets:
 5, 8,


SAMPLE RUN #2:
==============

Please enter N in the range [1,20]: 32
Please enter N in the range [1,20]: -1
Please enter N in the range [1,20]: 2

First set:   5, 3,
Second set:  8, 9,

There are no common numbers between the two sets.


SAMPLE RUN #3:
==============

Please enter N in the range [1,20]: 20

First set:   4, 0, 8, 1, 5, 5, 0, 1, 3, 3, 9, 4, 0, 2, 6, 0, 9, 4, 1, 0,
Second set:  9, 8, 6, 2, 8, 9, 9, 3, 4, 9, 7, 4, 7, 9, 5, 5, 2, 5, 6, 2,

The following numbers appear in both sets:
 2, 3, 4, 5, 6, 8, 9,

*/ 

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define DEBUG 0

void sortArray(int a[], int n)  // Selection sort (for debugging only)
{
	int i,j, minIndex;
	for(i=0; i<n-1; i++)
	{
		minIndex = i;
		for(j=i+1; j<n; j++) // find the minimum number in [i+1,...,n-1]
			if(a[j] < a[minIndex])
				minIndex = j;
				
		// do the swap
		int temp = a[i];
		a[i] = a[minIndex];
		a[minIndex] = temp;
	}
}

void printArray(int a[], int n)
{
	int i;
	for(i=0; i<n; i++) 
		printf("%2d,", a[i]);
}

int main(void)
{
	int i, N;

	int a[20]; // two arrays to store the two sets of numbers
	int b[20];
	
	srand ( time(NULL) );  // initialize the random number generator

	do
	{
		printf("Please enter N in the range [1,20]: ");
		scanf("%d",  &N);
	}while((N<1) || (N>20));
	
	for(i=0; i<N; i++) // ten numbers
	{
		a[i] = rand()%10;
		b[i] = rand()%10;
	}

	// Print the two sets of numbers (one per line)	
	printf("\nFirst set:  ");	printArray(a, N);
	printf("\nSecond set: ");	printArray(b, N);
	printf("\n");


	if(DEBUG)  // print the sorted arrays for debugging purposes
	{
		sortArray(a, N);
		sortArray(b, N);

		printf("\nSorted");
		printf("\nFirst set:  ");	printArray(a, N);
		printf("\nSecond set: ");	printArray(b, N);
		printf("\n");
	}

	
	// Idea: 
	// Start with another array c[10] that is initialized with zeros.
	// Go through the array a and for any number that appears there
	// make c[a[i]] = 1. This uses double indexing to do the calculation.
	// Then go through the array b and for any number that appears there
	// make c[b[i]]=2, but only if that element of c was already equal to 1
	// (i.e., only for the numbers that we know exist in the array a).
	
	int c[10];
	for(i=0; i<10; i++)
		c[i] = 0;
		
	for(i=0; i<N; i++)
		c[a[i]] = 1;

	int match = 0;  // Make this 1 if at least one matching number is found
	for(i=0; i<N; i++)
		if(c[b[i]] == 1)
		{
			c[b[i]] = 2;
			match = 1;
		}

	// print the results
	if(match == 0)
		printf("\n\nThere are no common numbers between the two sets.\n\n");
	else
	{
		printf("\n\nThe following numbers appear in both sets:\n");
		for(i=0; i<10; i++)
			if(c[i] == 2)
				printf("%2d,", i);
		printf("\n\n");
	}
	
    system("pause");
}