CareerCup

public int calculate(int num) {
while (num > 10) {
int curr_num = num;
num=0;
while (curr_num > 0) {
num += curr_num % 10;
curr_num = curr_num /10;
}
}
return num;
}

not sure but this might work.

int toBinarySearchTree (Node n) {

if ( n is leaf ) 
          return n.val;
   int leftChildVal= toBinarySearchTree(n.left);
   int rightChildVal= toBinarySearchTree(n.right);
   if (leftChildVal > n.val ) {
       replace n node and n.left node
   }
   if ( n.val < rightChildVal ) {
       replace n node and n.right node
   }

}

euclid s algorithm

int gcd ( int a, int b ) {
if ( b == 0 )
return a;
else return gcd ( b , a - b * ( a / b ) );

}