Daily LeetCode – day0124 0895. Maximum Frequency Stack

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

// 0895. Maximum Frequency Stack
class FreqStack {
    Map<Integer, Integer> cnt;
    Map<Integer, ArrayList<Integer>> stack;
    int maxFrequency;

    public FreqStack() {
        cnt = new HashMap<>();
        stack = new HashMap<>();
        maxFrequency = 0;
    }

    public void push(int val) {
        int valCnt = cnt.getOrDefault(val, 0) + 1;
        cnt.put(val, valCnt);
        if (valCnt > maxFrequency) {
            maxFrequency = valCnt;
            stack.put(maxFrequency, new ArrayList<>());
        }
        stack.get(valCnt).add(val);
    }

    public int pop() {
        int top = stack.get(maxFrequency).remove(stack.get(maxFrequency).size() - 1);
        cnt.put(top, cnt.get(top) - 1);
        if (stack.get(maxFrequency).size() == 0) {
            --maxFrequency;
        }
        return top;
    }
}

学习笔记：
这是一道久违的设计的题目。
要设计一个特殊的栈，所以当然不能只用栈了，还用到了hashmap和arraylist。