Detailed explanation of minimum stack

Introduction to minimum stack ：

Minimum stack is an algorithm idea , Can be in O(1) Get the minimum value of the whole stack in the time complexity of

Minimum stack idea ：

We need two stacks , One is the main stack , One is the smallest stack , If a number enters the main stack , Then we compare this number with the top element of the smallest stack , If it is smaller than the top element of the smallest stack , Then this number will be put into the minimum stack , Otherwise, put the top element of the minimum stack back into the minimum stack

subject ： Smallest stack  

link ：155. Smallest stack - Power button （LeetCode）

Title Description ：

Input ： 

Output ：

 

explain ：

 

Code ：

class MinStack {
public:
    stack<int> st, stt;
    MinStack() {
        
    }
    
    void push(int val) {
        st.push(val);
        if(stt.empty()){
            stt.push(val);
        }else{
            if(stt.top() > val){
                stt.push(val);
            }else{
                stt.push(stt.top());
            }
        }
    }
    
    void pop() {
        st.pop();
        stt.pop();
    }
    
    int top() {
        return st.top();
    }
    
    int getMin() {
        return stt.top();
    }
};

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