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;
}
}