SWE Interview preparation

https://leetcode.com/problems/merge-two-binary-trees/ Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not. You need to merge them into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value of the merged node. Otherwise, the NOT null node will be used as the node of new tree. Example 1: Input: Tree 1 Tree 2 1 2 / \ / \ 3 2 1 3 / \ \ 5 4 7 Output: Merged tree: 3 / \ 4 5 / \ \ 5 4 7   Note:  The merging process must start from the root nodes of both trees. ---

https://leetcode.com/problems/excel-sheet-column-title/ Given a positive integer, return its corresponding column title as appear in an Excel sheet. For example: 1 -> A 2 -> B 3 -> C ... 26 -> Z 27 -> AA 28 -> AB ... Example 1: Input: 1 Output: "A" Example 2: Input: 28 Output: "AB" Example 3: Input: 701 Output: "ZY" --- Related problems 171-excel-sheet-column-number ---

https://leetcode.com/problems/design-circular-queue/ Design your implementation of the circular queue. The circular queue is a linear data structure in which the operations are performed based on FIFO (First In First Out) principle and the last position is connected back to the first position to make a circle. It is also called "Ring Buffer". One of the benefits of the circular queue is that we can make use of the spaces in front of the queue. In a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. But using the circular queue, we can use the space to store new values. Your implementation should support following operations: MyCircularQueue(k) : Constructor, set the size of the queue to be k. Front : Get the front item from the queue. If the queue is empty, return -1. Rear : Get the last item from the queue. If the queue is empty, return -1. enQueue(value) : Insert an element into the circular queue. Re...

https://leetcode.com/problems/reverse-integer/ Given a 32-bit signed integer, reverse digits of an integer. Example 1: Input: 123 Output: 321 Example 2: Input: -123 Output: -321 Example 3: Input: 120 Output: 21 Note: Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−2 31 ,  2 31  − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows. --- Intuition Catch last digit Check overflow and underflow boundary condition update ans Time Complexity : O(log n) - number of digits Space Complexity : O(1) - Constant  ---

https://leetcode.com/problems/remove-linked-list-elements/ Remove all elements from a linked list of integers that have value  val . Example: Input: 1->2->6->3->4->5->6, val = 6 Output: 1->2->3->4->5 -- Intuition Have a prev pointer If head.val == target    Set the prev to head.next else    prev = prev.next Preprocess Corner case, while head.val == target at the beginning of list -- Related problems 237-delete-node-in-linked-list ---

https://leetcode.com/problems/spiral-matrix-ii/ Given a positive integer  n , generate a square matrix filled with elements from 1 to  n 2  in spiral order. Example: Input: 3 Output: [ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ] ] ---- Related problems 54-spiral-matrix ---

https://leetcode.com/problems/shortest-distance-to-a-character/ Given a string  S  and a character  C , return an array of integers representing the shortest distance from the character  C  in the string. Example 1: Input: S = "loveleetcode", C = 'e' Output: [3, 2, 1, 0, 1, 0, 0, 1, 2, 2, 1, 0] Note: S  string length is in  [1, 10000]. C  is a single character, and guaranteed to be in string  S . All letters in  S  and  C  are lowercase. ----

https://leetcode.com/problems/can-place-flowers/ Suppose you have a long flowerbed in which some of the plots are planted and some are not. However, flowers cannot be planted in adjacent plots - they would compete for water and both would die. Given a flowerbed (represented as an array containing 0 and 1, where 0 means empty and 1 means not empty), and a number  n , return if  n  new flowers can be planted in it without violating the no-adjacent-flowers rule. Example 1: Input: flowerbed = [1,0,0,0,1], n = 1 Output: True Example 2: Input: flowerbed = [1,0,0,0,1], n = 2 Output: False Note: The input array won't violate no-adjacent-flowers rule. The input array size is in the range of [1, 20000]. n  is a non-negative integer which won't exceed the input array size. --