C++

1class MinStack {
2  public:
3    stack<int> s1;
4
5    MinStack() {}
6
7    void push(int x) {
8      if(s1.empty()) {
9        s1.push(x);
10        s1.push(x);
11      } else {
12        int y = s1.top();
13        s1.push(x);
14        s1.push((y<x) ? y : x);
15      }
16    }
17
18    void pop() {
19      s1.pop();
20      s1.pop();
21    }
22
23    int top() {
24      int x = s1.top();
25      s1.pop();
26      int y = s1.top();
27      s1.push(x);
28      return y;
29    }
30
31    int getMin() {
32      return s1.top();
33    }
34};

Ruby

1class MinStack
2  def initialize()
3    @stack = []
4    @min = []
5  end
6
7  def push(val)
8    @stack.push(val)
9    @min.push(val) if @min.empty? or val <= @min[-1]
10  end
11
12  def pop()
13    @min.pop if @stack[-1] == @min[-1]
14    @stack.pop
15  end
16
17  def top()
18    @stack[-1]
19  end
20
21  def get_min()
22    @min[-1]
23  end
24end