[leedcode 155] Min 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.

class MinStack {
//使用两个栈，一个正常使用，一个保存已经压栈中最小的数，每次push和pop注意两个栈同时操作
private Stack<Integer> min=new Stack<Integer>();
private Stack<Integer> stack=new Stack<Integer>();
public void push(int x) {
stack.push(x);
if(min.empty()||x<min.peek()){//注意min判空
min.push(x);
}else{
min.push(min.peek());
}
}

public void pop() {
stack.pop();
min.pop();

}

public int top() {
return stack.peek();
}

public int getMin() {
return min.peek();

}
}