LeetCode 155. Min Stack

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.

https://leetcode.com/problems/min-stack/

class MinStack {
    //two stack
    Stack<int[]> stack = new Stack<>();
    public void push(int x) {
        if(stack.isEmpty()){
            stack.push(new int[]{x,x});
            return;
        }
        int min = stack.peek()[1];
        stack.push(new int[]{x,Math.min(x,min)});
    }
    public void pop(){
        stack.pop();
    }
    
    public int top(){
        return stack.peek()[0];
    }
    
    public int getMin(){
        return stack.peek()[1];
    }
}

Complexity:

Time complexity: O(1)

Space complexity: O(1)