Min-Stack.java

class MinStack {
    private Stack<Integer> mainStack;
    private Stack<Integer> minStack;
    public MinStack() {
        mainStack = new Stack<>();
        minStack = new Stack<>();
    }
    
    public void push(int val) {
       mainStack.push(val);
       if(minStack.isEmpty() || val<= minStack.peek()){
        minStack.push(val);
       }
    }
    
    public void pop() {
        if(mainStack.peek().equals(minStack.peek())){
            minStack.pop();
        }
       mainStack.pop();
    }
    
    public int top() {
        return mainStack.peek();
    }
    
    public int getMin() {
        return minStack.peek();
    }
}

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(val);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */