Leetcode•Oct 07, 2025

Min Stack

Hazrat Ali

Leetcode

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

Solution
/**
 */
class MinStack {
  constructor() {
    this.stack = [];
    this.min = null;
  }

  /**
   * @param {number} x
   * @return {void}
   */
  push(x) {
    if (this.stack.length === 0) {
      this.stack.push(x);
      this.min = x;
      return;
    }

    if (x < this.min) {
      this.stack.push(2 * x - this.min);
      this.min = x;
    } else {
      this.stack.push(x);
    }
  }

  /**
   * @return {number}
   */
  pop() {
    const x = this.stack.pop();

    if (x < this.min) {
      const result = this.min;
      this.min = 2 * this.min - x;
      return result;
    }

    if (this.stack.length === 0) {
      this.min = null;
    }

    return x;
  }

  /**
   * @return {number}
   */
  top() {
    const x = this.stack[this.stack.length - 1];

    if (x < this.min) {
      return this.min;
    }

    return x;
  }

  /**
   * @return {number}
   */
  getMin() {
    return this.min;
  }
}




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