Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

  • push(x) – Push element x onto stack.

  • pop() – Removes the element on top of the stack.

  • top() – Get the top element.

  • getMin() – Retrieve the minimum element in the stack.


思路：

用两个stack来实现，一个用来存放数据，一个用来放当前遇到的最小值，getMin就直接返回top。如果当前入/出栈的数据小于等于最小值，需要执行最小值入/出栈操作。

代码：

class MinStack {
public:
    void push(int x) {
        data.push(x);
        if(mins.empty() || x <= mins.top()) mins.push(x);
    }

    void pop() {
        if(data.empty()) return;
        if(mins.top() == data.top()) mins.pop();
        data.pop();
    }

    int top() {
        return data.top();
    }

    int getMin() {
        return mins.top();
    }
private:
    stack<int> data;
    stack<int> mins;
};