#895

Maximum Frequency Stack

expert · 1045 · lc hard +32 · 66.7% accepted · 4,942 likes · top 72%

Description

Design a stack that tracks element frequencies. Implement the FreqStack class:

- FreqStack() creates an empty stack.

- void push(int val) pushes integer val onto the stack.

- int pop() removes and returns the most frequently occurring element. Ties are broken by recency — the most recently pushed element among tied candidates is returned.

Example 1:

Input

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

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

Output

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

Example 2:

Explanation

FreqStack freqStack = new FreqStack();

freqStack.push(5); // The stack is [5]

freqStack.push(7); // The stack is [5,7]

freqStack.push(5); // The stack is [5,7,5]

freqStack.push(7); // The stack is [5,7,5,7]

freqStack.push(4); // The stack is [5,7,5,7,4]

freqStack.push(5); // The stack is [5,7,5,7,4,5]

freqStack.pop(); // return 5, as 5 is the most frequent. The stack becomes [5,7,5,7,4].

freqStack.pop(); // return 7, as 5 and 7 is the most frequent, but 7 is closest to the top. The stack becomes [5,7,5,4].

freqStack.pop(); // return 5, as 5 is the most frequent. The stack becomes [5,7,4].

freqStack.pop(); // return 4, as 4, 5 and 7 is the most frequent, but 4 is closest to the top. The stack becomes [5,7].

Code

class FreqStack:

    def __init__(self):
        

    def push(self, val: int) -> None:
        

    def pop(self) -> int:
        


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

class FreqStack:

    def __init__(self):
        

    def push(self, val: int) -> None:
        

    def pop(self) -> int:
        


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