Programming problem: Min Stack

Question

Design a stack class that supports the push, pop, top, and getMin operations.

• 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.

Each function should run in O(1) time.

Example

Input: ["MinStack", "push", 1, "push", 2, "push", 0, "getMin", "pop", "top", "getMin"]

Output: [null,null,null,null,0,null,2,1]

Explanation:
MinStack minStack = new MinStack();
minStack.push(1);
minStack.push(2);
minStack.push(0);
minStack.getMin(); // return 0
minStack.pop();
minStack.top(); // return 2
minStack.getMin(); // return 1

Constraints

• -2^31 <= val <= 2^31 - 1.
• pop, top and getMin will always be called on non-empty stacks.

Solution

class MinStack {
  value: number[] = [];

  push(val: number): void {
    this.value[this.value.length] = val;
  }

  pop(): void {
    const nextValue: number[] = [];

    for (let i = 0; i < this.value.length - 1; i++) {
      nextValue[i] = this.value[i];
    }

    this.value = nextValue;
  }

  top(): number {
    return this.value[this.value.length - 1];
  }

  getMin(): number {
    let min: number = this.value[0];

    for (const val of this.value) {
      min = Math.min(min, val);
    }

    return min;
  }
}