Problems

Q1: Implement Queue using Stacks

Approach # 01 Using 2 Stacks

1. Step 1: Push S1 elements into S2.

2. Step 2: Push the Given input element in the S1 stack.

3. Step 3: Push S2 elements into S1.

Queue using 2 Stacks

class MyQueue {
    stack <int> s1, s2;
public:
    
    void push(int x) {
        while(!s1.empty()) {
            s2.push(s1.top());
            s1.pop();
        }

        s1.push(x);
        
        while(!s2.empty()){
            s1.push(s2.top());
            s2.pop();
        }
    }
    
    int pop() {
        if(empty())return -1;
        
        int d = s1.top();
        s1.pop();
        return d;

    }
    
    int peek() {
        if(empty()) return -1;

        return s1.top();
    }
    
    bool empty() {
        return s1.empty();
    }
};

Approach # 02 Using Single Stack

class MyQueue {
    stack <int> s1;
public:
    
    void push(int x) {
        insertAtBottom(x);
    }
    
    void insertAtBottom(const int x) {
        // base condition
        if(s1.empty()) {
            s1.push(x);
            return ;
        }
        
        int temp = s1.top();
        s1.pop();
        
        // recursive call
        insertAtBottom(x);
        
        s1.push(temp);
    }
    
    int pop() {
        if(empty())return -1;
        
        int d = s1.top();
        s1.pop();
        return d;

    }
    
    int peek() {
        if(empty()) return -1;

        return s1.top();
    }
    
    bool empty() {
        return s1.empty();
    }
};

Q2: Reverse Queue using recursion

void reverseQueue(queue<int>& q1) {
    if(q1.empty()) return ;

    int temp = q1.front();
    q1.pop();
    reverseQueue(q1);

    q1.push(temp);
}

void print(queue<int> q) {
    while(!q.empty()) {
        cout << q.front() << " ";
        q.pop();
    }cout << endl;
} 

Q3: Check Palindrome

bool checkPalindrome(string s) {
    queue<char> q1, q2;
    int i = 0;6
    for (; i < s.size()/2; i++)
    {
        q1.push(s[i]);
    }
    
    if(s.size()&1) i++;

    for(int j = s.size()-1; j >= i; j--) {
        q2.push(s[j]);
    }    
    return q1 == q2;
}