781. Rabbits in Forest

There is a forest with an unknown number of rabbits. We asked n rabbits “How many rabbits have the same color as you?” and collected the answers in an integer array answers where answers[i] is the answer of the ith rabbit.

Given the array answers, return the minimum number of rabbits that could be in the forest.

class Solution {
public:
    int numRabbits(vector<int>& answers) {
        unordered_map<int, int> freq;
        for(auto& a : answers) freq[a]++;
        int res = 0;
        
        for(auto& [k, v] : freq) {
            int req = k + 1;
            res += max(1.0, ceil(1.0 * v / req)) * req;
        }
        
        return res;
    }
};