[Solved] Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Question

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Implement the MinStack class:

  • MinStack() initializes the stack object.
  • void push(int val) pushes the element val onto the stack.
  • void pop() removes the element on the top of the stack.
  • int top() gets the top element of the stack.
  • int getMin() retrieves the minimum element in the stack.

You must implement a solution with O(1) time complexity for each function.

Example 1:

Input
["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]

Output

[null,null,null,null,-3,null,0,-2]

Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2

Constraints:

  • -231 <= val <= 231 - 1
  • Methods poptop and getMin operations will always be called on non-empty stacks.
  • At most 3 * 104 calls will be made to pushpoptop, and getMin.

Python Solution

class MinStack:

    def __init__(self):
        """
        initialize your data structure here.
        """
        self.stack = []
        

    def push(self, x: int) -> None:
        cur_min = self.getMin()
        if cur_min==None or cur_min > x:
            cur_min = x
        self.stack.append([x,cur_min])

    def pop(self) -> None:
        self.stack.pop()

    def top(self) -> int:
        if len(self.stack)==0:
            return None
        return self.stack[-1][0]

    def getMin(self) -> int:
        if len(self.stack)==0:
            return None
        return self.stack[-1][1]

# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(x)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()
Abhishek Sharma
Abhishek Sharma

Started my Data Science journey in my 2nd year of college and since then continuously into it because of the magical powers of ML and continuously doing projects in almost every domain of AI like ML, DL, CV, NLP.

Articles: 514

Leave a Reply

Your email address will not be published. Required fields are marked *