Package g0801_0900.s0895_maximum_frequency_stack

Class FreqStack

java.lang.Object
g0801_0900.s0895_maximum_frequency_stack.FreqStack
public class FreqStack extends java.lang.Object
895 - Maximum Frequency Stack.

Hard

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.
  • void push(int val) pushes an integer val onto the top of the stack.
  • int pop() removes and returns the most frequent element in the stack.
    • If there is a tie for the most frequent element, the element closest to the stack’s top is removed and 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]

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].

Constraints:

  • 0 <= val <= 109
  • At most 2 * 104 calls will be made to push and pop.
  • It is guaranteed that there will be at least one element in the stack before calling pop.

  • Constructor Summary

    Constructors
    Constructor
    Description
    FreqStack()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    pop()
     
    void
    push(int val)
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • FreqStack

      public FreqStack()

  • Method Details

    • push

      public void push(int val)

    • pop

      public int pop()