【剑指offer】包含min函数的栈

import java.util.Stack;

public class Program_21 {
Stack<Integer> data_s = new Stack<Integer>();// 保存元素数据
Stack<Integer> min_s = new Stack<Integer>();// 保存最小值

public void push(int node) {
data_s.push(node);
if (min_s.size() == 0 || node < top()) {
min_s.push(node);
} else {
min_s.push(top());
}
}

public void pop() {
if (data_s.size() != 0 && min_s.size() != 0) {
data_s.pop();
min_s.pop();
}
}

public int top() {
if (min_s.size() == 0) {
return -1;
}
return min_s.peek();
}

public int min() {
if (min_s.size() != 0) {
return top();
}
return -1;
}
}