An implementation of a queue Q, using two stacks S1 and S2, is given below:

void insert(Q, X){
  push(S1, X);
}

void delete(Q){
 if(stack - empty(S1)) then {
   print("Q is empty");
   return;
 }else while (!(stack - empty(S1))){
   X = pop(S1);
   push(S2, X);
 }
 X = pop(S2);
}

Let n insert and $$m( \le n)$$ delete operations be performed in an arbitrary order on an empty queue Q. Let x and y be the number of push and pop operations performed respectively in the process. Which one of the following is true for all m and n?

The following function computes the value of ^mC_n correctly for all legal values m and n (m≥1,n≥0 and m>n)

int func(int m, int n) 
{ 
     if (E) return 1; 
     else return(func(m -1, n) + func(m - 1, n - 1)); 
} 

In the above function, which of the following is the correct expression for E?

Assume that the operators +, -, ×, are left associative and ^ is right associative. The order of precedence (from highest to lowest) is ^, ×, +, -. The postfix expression corresponding to the infix expression a + b×c-d^e^f is

A program attempts to generate as many permutation as possible of the string “abcd” by pushing the character a,b,c,d in the same order onto a stack, but it may pop off the top character at any time. Which one of the following a strings CANNOT be generated using this program?