std::set and Sorted Unique Collections

Automatic Uniqueness and Sorting

#include <set>

set<int> s = {5, 2, 8, 2, 1, 5};
// Stored as: {1, 2, 5, 8} — sorted, no duplicates

s.insert(3);            // {1,2,3,5,8}
s.erase(2);             // {1,3,5,8}
s.count(3)              // 1 (present)
s.count(99)             // 0 (absent)

for (int x : s) cout << x;  // always sorted

Use cases

• Membership tests (fast O(log n) with set, O(1) with unordered_set)
• Keeping a sorted unique list
• Finding intersections/unions

Your Task

Write intersection(vector<int> a, vector<int> b) that returns a sorted vector of elements present in both inputs, with no duplicates in the result.