Method push

src/class015/GetMinStack.java:19–26

(int val)

		}

		public void push(int val) {
			data.push(val);
			if (min.isEmpty() || val <= min.peek()) {
				min.push(val);
			} else { // !min.isEmpty() && val > min.peek()
				min.push(min.peek());
			}
		}

		public void pop() {
			data.pop();