https://www.interviewbit.com/problems/min-stack/

InterviewBit:Min Stack

struct Node{
    int val;
    struct Node * next;
    struct Node * nextMin;
    Node(int v){
        val = v;
        next = NULL;
        nextMin = NULL;
    }
};

struct Node* head = NULL;
struct Node* minElement = NULL;

MinStack::MinStack() {
    head = NULL;
    minElement = NULL;
}

void MinStack::push(int x) {
    
    if(head==NULL){
        head = new Node(x);
        minElement = head;
    }else{
        Node* temp = new Node(x);
        temp->next = head;
        head = temp;
        if(head->val < minElement->val){
            head->nextMin = minElement;
            minElement = head;
        }
    }
    
}

void MinStack::pop() {
    if(head!=NULL){
        if(head==minElement){
            minElement = minElement->nextMin;
        }
        Node* temp = head;
        head = head->next;
        delete temp;
    }
}

int MinStack::top() {
    if(head!=NULL){
        return head->val;
    }else{
        return -1;
    }
}

int MinStack::getMin() {
    if(minElement==NULL){
        return -1;
    }else{
        return minElement->val;
    }
}