一.解法

https://leetcode-cn.com/problems/min-stack/
要点：辅助栈
Python，C++，Java都用了相同的辅助栈法，顾名思义就是有个栈放在原来栈旁边执行相关的操作，使得每个元素 a 与其相应的最小值 m 时刻保持一一对应。因此我们可以使用一个辅助栈，与元素栈同步插入与删除，用于存储与每个元素对应的最小值。

二.Python实现

class MinStack:
    def __init__(self):
        self.stack = []
        self.min_stack = [math.inf]

    def push(self, x: int) -> None:
        self.stack.append(x)
        self.min_stack.append(min(x, self.min_stack[-1]))

    def pop(self) -> None:
        self.stack.pop()
        self.min_stack.pop()

    def top(self) -> int:
        return self.stack[-1]

    def getMin(self) -> int:
        return self.min_stack[-1]



# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(x)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()

三.C++实现

class MinStack {
public:
    /** initialize your data structure here. */
    MinStack() {
        
    }
    
    stack<int> a;
    stack<int> min;
    
    void push(int x) {
        a.push(x);
        if(min.empty()||x<=min.top()) min.push(x);
    }
    
    void pop() {
        if(a.top()==min.top()) min.pop();
        a.pop();
    }
    
    int top() {
       return a.top();
    }
    
    int getMin() {
        return min.top();
    }
};

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack* obj = new MinStack();
 * obj->push(x);
 * obj->pop();
 * int param_3 = obj->top();
 * int param_4 = obj->getMin();
 */

四.java实现

class MinStack {
    private Stack<Integer> stack;
    private Stack<Integer> min_stack;
    public MinStack() {
        stack = new Stack<>();
        min_stack = new Stack<>();
    }
    public void push(int x) {
        stack.push(x);
        if(min_stack.isEmpty() || x <= min_stack.peek())
            min_stack.push(x);
    }
    public void pop() {
        if(stack.pop().equals(min_stack.peek()))
            min_stack.pop();
    }
    public int top() {
        return stack.peek();
    }
    public int getMin() {
        return min_stack.peek();
    }
}



/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(x);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */