Check if two given sets are disjoint?

Two sets are disjoint set when they have no common elements. In other words, if we get the intersection of two sets, then we will get null set.

The method is simple, in this algorithm, two sets are given. We assume that both sets are already sorted, items are compared between two sets. when there is a match, then it is not a disjoint set, when no items are matched, they are disjoint sets.

Input and Output

Two sets:
set1: {15, 12, 36, 21, 14}
set2: {7, 89, 56, 32}
Both sets are disjoint


isDisjoint(set1, set2)

Input: Two sets.

Output: True when both sets are disjoint.

   i1 := start of first set
   i2 := start of second set
   while i1 in set1 and i2 in set 2, do
      if set1[i1] < set2[i2], then
         i1 := i1 + 1
      else if set2[i2] < set1[i1], then
         i2 := i2 + 1
         return false
   return true


using namespace std;

bool isDisjoint(set<int> set1, set<int> set2) {
   set<int>::iterator i1, i2;
   i1 = set1.begin(); i2 = set2.begin();            //initialize iterators with first element
   while(i1 != set1.end() && i2 != set2.end()) {         //when both set have some elements to check
      if(*i1 < *i2)
         i1++;                   //when item of first set is less than second set
      else if(*i2 < *i1)
         i2++;               //when item of second set is less than first set
         return false;            //if items are matched, sets are not disjoint
   return true;


int main() {
   set<int> set1, set2;
   int n1, n2;
   cout << "Enter number of elements in set 1: "; cin >>n1;

   while(n1 != set1.size()) {       //duplicate items will be discarded
      int item;
      cout << "Enter element: "; cin >> item;

   cout << "Enter number of elements in set 2: "; cin >>n2;
   while(n2 != set2.size()) {
      int item;
      cout << "Enter element: "; cin >> item;

   if(isDisjoint(set1, set2))
      cout << "Both sets are disjoint";
      cout << "Sets are not disjoint";


Enter number of elements in set 1: 5
Enter element: 15
Enter element: 12
Enter element: 36
Enter element: 21
Enter element: 14
Enter number of elements in set 2: 4
Enter element: 7
Enter element: 89
Enter element: 56
Enter element: 32
Both sets are disjoint

Updated on: 17-Jun-2020


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