assignment

Question

Following C program is written to find the pairs of elements in an array whose sum is 9.

The for loop will iterate over the array of size 7.

The program will print the correct pairs (whose sum is 9) on iteration number ‘a’ and ‘b’.

What are the values of ‘a’ and ‘b’?  Note: for 1st iteration, i=0. For 2nd iteration, i=1 and so on.

 

#include<stdio.h>
#define MAX 10
void pair(int *A, int size, int sum)
{

   int i,j;
   int B[MAX]={0};
   for(i=0;i<size;i++)
   { 
        j= sum - A[i];
       if(j>=0 && B[j] == 1)
            printf("Sum is 9 for :%d %d\n",A[i],j);
        B[A[i]] = 1;
   }
}
void main()
{
   int sum = 9;    
   int A[7]={1,4,3,3,5,2,6};
   pair(A,7,sum);
}

1. 5,7

2. 2,5

3. 4,6

4. 2,3

Comments

cn someone plzz explain what is B[MAX]={0} and B[A[i]] = 1 if possible can explain the execution of the program

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the limitation in this program is MAX.

So, A[i] < MAX

Note :- if SUM  > (MAX-1) + (MAX-1) then no pair is matching with that !

Answer 1

the concept behind this question is :-

B[MAX] ---> is array which have indices from 0 to MAX-1

where B[1] represents, is 1 present in the given i/p array or not ?

where B[4] represents, is 4 present in the given i/p array or not ?

in general, where B[k] represents, is "k" present in the given i/p array or not ?

i mean if B[k] = 1, we have k in the given i/p array.

 

coming to the pair() function :-

i indicates the index in the given i/p array ==> a[i] represent the element in the array.

on every iteration, we calculate the value of  j= sum - A[i]; ==> it means we are looking as A[i]+j = sum.

( Note that i is index but j is variable. )

condition i :-    j ≥ 0 means, the value present at the index i, should be ≤ required sum.

condition ii :-  B[j] == 1, checks that the value j is present in the given i/p array.

if these two conditions satisfies then print the values.

 

B[A[i]] = 1; ----> due to this line, we are " A[i] value is present in the i/p array "

i mean to say, if i=0, A[i]=1 ===> B[1] = 1 ===> it means we have 1 in the i/p array.

 

PS : from here onwards you can solve this problem easily. So don't look following continuation !

if you still didn't get it, then check it !!

 

i/p array :-  A[7]={1,4,3,3,5,2,6}

when i = 0, j=sum-A[i] = 9-1 = 8, condition fails, due to line B[A[i]] = 1; we kept B[1] = 1, means we have 1 in the i/p array.

when i = 1, j=sum-A[i] = 9-4 = 5, condition fails, due to line B[A[i]] = 1; we kept B[4] = 1, means we have 4 in the i/p array.

when i = 2, j=sum-A[i] = 9-3 = 6, condition fails, due to line B[A[i]] = 1; we kept B[3] = 1, means we have 3 in the i/p array.

when i = 3, j=sum-A[i] = 9-3 = 6, condition fails, due to line B[A[i]] = 1; we kept B[3] = 1, means we have 3 in the i/p array.

when i = 4, j=sum-A[i] = 9-5 = 4, condition SUCCESS, due to B[4]=1, So the pair is 4 and 5 and due to line B[A[i]] = 1; we kept B[5] = 1, means we have 5 in the i/p array.

when i = 5, j=sum-A[i] = 9-2 = 7, condition fails, due to line B[A[i]] = 1; we kept B[2] = 1, means we have 2 in the i/p array.

when i = 6, j=sum-A[i] = 9-6 = 3, condition SUCCESS, due to B[3]=1, So the pair is 3 and 6 and due to line B[A[i]] = 1; we kept B[6] = 1, means we have 6 in the i/p array.

required answer :- a=4 and b=6

Comments

require answer is 5,7

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is a[7] is present ?

no need to match the answers.... just understand the concept !

if you want to match the answers, i hope their index starts with 1 but not 0.