2598. Smallest Missing Non-negative Integer After Operations

You are given a 0-indexed integer array nums and an integer value.

In one operation, you can add or subtract value from any element of nums.

• For example, if nums = [1,2,3] and value = 2, you can choose to subtract value from nums[0] to make nums = [-1,2,3].

The MEX (minimum excluded) of an array is the smallest missing non-negative integer in it.

• For example, the MEX of [-1,2,3] is 0 while the MEX of [1,0,3] is 2.

Return the maximum MEX of nums after applying the mentioned operation any number of times.

class Solution {
public:
    int findSmallestInteger(vector<int>& A, int value) {
        int res = 0;
        unordered_map<int, int> x;
        for(auto a : A)  {
            if(a >= 0) x[a%value] += 1;
            else {
                a %= value;
                x[(a + value)  % value]+=1;
            }
        }
        while(x[res % value]) {
            x[res%value] -= 1;
            res += 1;
        }
        return res;
    }
};