leetcode 155. Min Stack

https://leetcode.com/problems/min-stack/#/description 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. Example: MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); –> Returns -3. minStack.pop(); minStack.top(); –> Returns 0. minStack.getMin(); –> Returns -2.
最小値を1つのstackで保存

class MinStack {
public:
    /** initialize your data structure here. */

        stack<int> s1;
        stack<int> s2;


    void push(int x) {
        s1.push(x);
        if(s2.empty()||x<=s2.top())
        {
            s2.push(x);
        }
    }

    void pop() {
        int top = s1.top();
        s1.pop();
        if(!s2.empty()&&top==s2.top())
        {
            s2.pop();
        }
    }

    int top() {
        return s1.top();
    }

    int getMin() {
        return s2.top();
    }
};