leetcode_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.

 Stack<Integer> st = new Stack<Integer>();
	Stack<Integer> stMin = new Stack<Integer>();
	int min = 0;

	public void push(int x) {
		if (!st.isEmpty()) {
			if (min > x) {
				st.push(x);
				stMin.push(x);
				min = x;
			} else {
				st.push(x);
				stMin.push(min);
			}

		} else {
			st.push(x);
			stMin.push(x);
			min = x;
		}
	}

	public void pop() {
		st.pop();
		stMin.pop();
		if (!stMin.isEmpty())//元素出栈时要记着更新当前栈中的最小值
			min = stMin.peek();

	}

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

	public int getMin() {
		return stMin.peek();
	}