using distance to keep track of the min in a stack

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

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• getMin() -- Retrieve the minimum element in the stack.

 

Example:

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> Returns -3.
minStack.pop();
minStack.top();      --> Returns 0.
minStack.getMin();   --> Returns -2.

public class MinStack {
    
    int min;
    Stack<Integer> stack;

    /** initialize your data structure here. */
    public MinStack() {
        stack = new Stack<>();
    }
    
    public void push(int x) {
        if(stack.isEmpty()){
            min = x;
            stack.push(0);     
        }else{
            stack.push(x-min);
            if(x < min) min = x;
        }
    }
    
    public void pop() {
        if(stack.isEmpty()) return;
        else{
            int pop = stack.pop();
            if(pop < 0) min = min -pop;
        }
    }
    
    public int top() {
        int top = stack.peek();
        if(top < 0) return min;
        else{
            return min + top;
        }
        
    }
    
    public int getMin() {
        return min;
    }
}