举例让抽象问题具体化：包含min函数的栈

import java.util.Stack;

public class Solution {

Stack<Integer> dataStack = new Stack<Integer>();
Stack<Integer> minStack = new Stack<Integer>();

public void push(int node) {
Integer temp = new Integer(node);
dataStack.push(temp);
if (minStack.empty()) {
minStack.push(temp);
} else {
int min = minStack.peek().intValue();
if (node > min) {
minStack.push(minStack.peek());
} else {
minStack.push(temp);
}
}
}

public void pop() {
dataStack.pop();
minStack.pop();
}

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

public int min() {
return minStack.peek();
}
}