155_Min_Stack.java

//
// 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.
//
//


class MinStack {

    /** initialize your data structure here. */
        List <Integer> stack =new ArrayList<>();
        int count=0;
    public MinStack() {

    }
    
    public void push(int x) {
               stack.add(x);
               count++;
    }
    
    public void pop() {
          count--;
        stack.remove(count);
      
    }
    
    public int top() {
        return stack.get(count-1);
    }
    
    public int getMin() {
        int min=stack.get(0);
        for(int i=1;i<stack.size();i++){
            if(stack.get(i)<min){
                min=stack.get(i);
            }
        }
        return min;
    }
}

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