Preqin Software Engineer Interview Questions and Answers

Find an odd occurring number among even occurring numbers.

• Use XOR operation to cancel out even occurring numbers and get the odd occurring number.

• Iterate through the array and XOR each element with the result variable.

• The final result will be the odd occurring number.

Print the spiral order of a binary tree and matrix.

• For binary tree, use level order traversal and alternate direction for each level.

• For matrix, use four pointers to traverse in spiral order.

• Example for binary tree: 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> 8 -> 9

• Example for matrix: 1 2 3 4 -> 8 7 6 5 -> 9 10 11 12 -> 16 15 14 13

Finding pairs in an array with a given sum.

• Iterate through the array and for each element, check if the difference between the given sum and the element exists in the array.

• Use a hash table to store the elements of the array and their indices for faster lookup.

• If there are multiple pairs with the same sum, return any one of them.

• If no pair is found, return null or an empty array.

Find total number of k element with given avg in an array in minimum time complexity.

• Use sliding window technique to traverse the array in O(n) time complexity.

• Maintain a sum variable to keep track of the sum of elements in the window.

• If the sum of elements in the window is equal to k times the given avg, increment the count.

• Move the window by subtracting the first element and adding the next element in the array.

Printing non-boundary elements of a binary tree

• Traverse the tree in any order (preorder, inorder, postorder)

• Check if the current node is not a boundary node (not the first or last node in its level)

• If it is not a boundary node, print its value

• Recursively traverse its left and right subtrees