Set Operations

Implementation of set operations like union, intersection, difference and set membership.

Union Operation :

To get the union of two arrays, apply merge procedure such that if an element is present in both arrays, copy it to the merged array once and increment both i and j.
void unionOfArray(int a[], int b[], int c[], int n1, int n2) {
// Index pointers
int i = 0, j = 0, k= 0;
while (i < n1 && j < n2) {
// If elements are same, copy once and increment all
if (a[i] == b[j]) {
c[k] = a[i];
i++;
j++;
} else if (a[i] < b[j]) {
c[k] = a[i];
i++;
} else {
c[k] = b[j];
j++;
}
k++;
}
// Copy remaining elements from first array
while (i < n1) {
c[k] = a[i];
i++;
k++;
}
// Copy remaining elements from second array
while (j < n2) {
c[k] = b[j];
j++;
k++;
}
​
}

Intersection Operation :

In intersection operation, apply merge procedure in such a manner that the elements are copied only if they are the same or else, their index pointers should just be incremented. Leftover elements will not be considered.
void intersection(int a[], int b[], int c[], int n1, int n2) {
​
int i = 0, j = 0, k= 0;
while (i < n1 && j < n2) {
// Increment all index pointers if element is same
if (a[i] == b[j]) {
c[k] = a[i];
i++;
j++;
k++;
} else if (a[i] < b[j]) {
i++;
} else {
j++;
}
}
​
}

Difference Operation :

The difference operation or A-B operation will also follow the merge procedure but in such a manner that elements will only be copied from the first array and that too only if it is not present in the second array.
void difference(int a[], int b[], int c[], int n1, int n2) {
​
int i = 0, j = 0, k= 0;
while (i < n1 && j < n2) {
// If elements are same, just increment i and j
if (a[i] == b[j]) {
i++;
j++;
} else if (a[i] < b[j]) {
// If element is not same and present in first array,
// copy it and increment i and k.
c[k] = a[i];
i++;
k++;
} else {
// If element is in second array, just increment j.
j++;
}
}
// Copy remaining elements from first array
while (i < n1) {
c[k] = a[i];
i++;
k++;
}
​
}

Set Membership :

For set membership operation, just implement binary search or linear search.
Contributed by Nitin Ranganath