2834. Find the Minimum Possible Sum of a Beautiful Array

You are given positive integers n and target.

An array nums is beautiful if it meets the following conditions:

• nums.length == n.
• nums consists of pairwise distinct positive integers.
• There doesn’t exist two distinct indices, i and j, in the range [0, n - 1], such that nums[i] + nums[j] == target.

Return the minimum possible sum that a beautiful array could have.

class Solution {
public:
    long long minimumPossibleSum(int n, int target) {
        unordered_set<long long> exc; 
        long long res = 0;
        for(long long i = 1, cnt = 0; cnt < n; i++) {
            if(exc.count(i)) continue;
            res += i;
            exc.insert(target - i);
            cnt += 1;
        }
        return res;
    }
};