롤케이크 자르기

https://school.programmers.co.kr/learn/courses/30/lessons/132265

import java.util.*;

class Solution {
    public int solution(int[] topping) {
        int answer = 0;
        
        HashMap<Integer, Integer> right = new HashMap<>();
        for(int t : topping)
        {
            right.put(t, right.getOrDefault(t, 0)+1);
        }
        
        HashMap<Integer, Integer> left = new HashMap<>();
        for(int t : topping)
        {
            left.put(t, left.getOrDefault(t, 0)+1);
            if(right.containsKey(t))
            {
                int cnt = right.get(t)-1;
                if(cnt > 0)
                    right.put(t, cnt);
                else
                    right.remove(t);
                
            }
                
            if(left.size() == right.size())
                answer++;
        }
        
        return answer;
    }
}