12 · Min Stack - LintCode

# Description

Implement a stack with following functions:

All above should be in O(1) cost

min() will never be called when there is no number in the stack.

# Example

Example 1:

Input:

push(1)
min()
push(2)
min()
push(3)
min()

Output:

1
1
1

	public class MinStack {
	private Stack<Integer> stack;
	private Stack<Integer> minStack;
	public MinStack() {
	stack = new Stack<>();
	minStack = new Stack<>();
	}

	/*
	* @param number: An integer
	* @return: nothing
	*/
	public void push(int number) {
	stack.push(number);
	if (minStack.isEmpty()) {
	minStack.push(number);
	} else {
	int min = Math.min(minStack.peek(), number);
	minStack.push(min);
	}
	}

	/*
	* @return: An integer
	*/
	public int pop() {
	minStack.pop();
	return stack.pop();

	}

	/*
	* @return: An integer
	*/
	public int min() {
	return minStack.peek();
	}
	/*
	public int top() {
	return stack.peek();
	}
	*/
	}