Medium Top Interview

Question 1

Permutations of numbers

Answer 1

depth first search for each element

Question 2

Generate parentheses

Answer 2

Back tracking and depth first search, two recursive calls

Question 3

238. Product of Array Except Self

Answer 3

Take leftside product and right side product and multiply them together.

Question 4

78. Subsets

Answer 4

Recursion and backtracking

Question 5

230. Kth Smallest Element in a BST

Answer 5

Keep a stack. Push all left elements, if k is zero, return, else decrement k and go right.

Question 6

4Sum II

Answer 6

hashtable

Question 7

48. Rotate Image

Answer 7

rotate a[i][j] = a[j][i] and then reverse the individual rows

Question 8

Find duplicate element in the array

Answer 8

fast and slow method. However fast is basically a[a[fast]] instead of next next

Question 9

347. Top K Frequent elements

Answer 9

Create a dict, rev dict and a min heap.