Maximum Frequency Stack — LeetCode 895 Python Solution

The problem

Design a stack-like data structure to push elements to the stack and pop the most frequent element from the stack. Implement the FreqStack class: FreqStack() constructs an empty frequency stack.

Example

Input

["FreqStack", "push", "push", "push", "push", "push", "push", "pop", "pop", "pop", "pop"]

Output

[null, null, null, null, null, null, null, 5, 7, 5, 4]

Explanation

FreqStack freqStack = new FreqStack();

Python solution

class FreqStack:
    def __init__(self):
        self.cnt = defaultdict(int)
        self.q = []
        self.ts = 0

    def push(self, val: int) -> None:
        self.ts += 1
        self.cnt[val] += 1
        heappush(self.q, (-self.cnt[val], -self.ts, val))

    def pop(self) -> int:
        val = heappop(self.q)[2]
        self.cnt[val] -= 1
        return val


# Your FreqStack object will be instantiated and called as such:
# obj = FreqStack()
# obj.push(val)
# param_2 = obj.pop()

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 895. Maximum Frequency Stack is filed here because LeetCode tags it Stack, which is the vocabulary this hub collects.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

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