#x Problem Solving Questions

Questions

Here is a non-exhaustive list of problem-solving questions.

Pre-read:
- Time and Space Complexity
- Big O CheatSheet
  - Worst case scenario to be considered when benchmarking
- If Java is your programming language to solve, here is the Collections framework overview chart

Questions #

1	fizz-buzz
2	Warmup-2 > stringYak	HINT: Scan char by char having condition like if “yak” is found jump the pointer to 3 chars at once
3	Warmup-2 > last2	HINT: use substring and equals() Question description is confusing. Focus on sample input and output. Count the last 2 chars substring in given string except the last 2chars.
4	Warmup-2 > arrayCount9	HINT: Use 2-pointer
5	Warmup-2 > countXX
6	Warmup-2 > stringX
7	Warmup-2 > has271	HINT: `Math.abs(third - (first-1)) <= 2`
8	Warmup-2 > altPairs	HINT: Jump by 2 chars but ensure there is no `java.lang.StringIndexOutOfBoundsException`
9	String1 > minCat
10	String-1 > without2	HINT: With overlapping sample input and output `XXX -> "x"`. Handle Edge cases: Single char strings like “” or “x”
11	String-1 > startWord
12	String-2 > xyzThere	HINT: Repetition possible. Example: `abc.xyzxyz`
13	String-1 > withoutX
14	String-1 > withoutX2
15	minimum-moves-to-equal-array-elements
16	minimum-moves-to-equal-array-elements-ii
17	longest-happy-string
18	fibonacci-number
19	reverse-integer

NOTE: In math division we have 2 parts - remainder and quotient. In programming we use

% operator to find the remainder and
/ operator to find the quotient
Example Algorithm/pseudocode

Given a number 123

Divide by 10

123 / 10 = 12(quotient)

123 % 10 = 3(remainder)

initialize 3 vars reverse=0, remainder=0, number=123

while(number != 0) {
    remainder = number % 10;
    reverse = reverse*10 + remainder;
    number /= 10;
}

Finally, the reverse var has the reversed value

20	gcd-of-two-numbers	Refer Algorithm: Euclidian Algorithm
21	armstrong-number Alternative Link: armstrong-numbers
22	palindrome-number Note: Solve it without converting the input to String
23	Give a string in form of char[] reverse it in place Note: Solve it in-place	HINT: 2 pointers at front and back, break the loop when i < j and swap chars
24	two-sum
25	three-sum
26	contains-duplicate
27	valid-anagram
28	Valid Parentheses	HINT: `java.util.Stack`(push, peek, pop) + `switch` statement
29	kth-largest-element-in-an-array Note: Solve it without Sorting	HINT: with `offer()` load the given array into PriorityQueue(ADT)(Initialize the priority queue as max-heap passing `Comparator.reverseOrder()`) and `poll()` the head k times
30	best-time-to-buy-and-sell-stock
31	Reverse a Linked list

Linked List Insertion:
Linked List Reversal:

32	Remove Linked List elements
33	Move Zeros
34	Max Sub array sum
35	Top k Frequent elements
36	Rotate array to right k steps
37	LRU Cache

HINT:

Option1: LinkedList(Is a Doubly LinkedList in Java) + HashMap
Option2:

  int capacity = 2;
  LinkedHashMap<Integer, Integer> lhs =
  new LinkedHashMap<>(capacity, 0.75f, true) {

    @Override
    protected boolean removeEldestEntry(java.util.Map.Entry<Integer, Integer> eldest) {
      return size() > capacity;
    }
  };

38	Reverse words in a string
39	Reverse Words
40	Array-1 > unlucky1

References #

NeetCode practice