#x Problem Solving 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 > last2	Question description is confusing. Focus on sample input and output. Count the last 2 chars substring in given string except the last 2chars
3	Warmup-2 > arrayCount9	HINT: Use 2-pointer
4	Warmup-2 > countXX
5	Warmup-2 > stringX
6	Warmup-2 > has271
7	Warmup-2 > altPairs
8	String1 > minCat
9	String-1 > without2
10	String-1 > startWord
11	String-1 > withoutX
12	String-1 > withoutX2
13	minimum-moves-to-equal-array-elements
14	minimum-moves-to-equal-array-elements-ii
15	longest-happy-string
16	fibonacci-number
17	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

18	gcd-of-two-numbers	Refer Algorithm: Euclidian Algorithm
19	armstrong-number Alternative Link: armstrong-numbers
20	palindrome-number Note: Solve it without converting the input to String
21	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
22	two-sum
23	three-sum
24	contains-duplicate
25	valid-anagram
26	Valid Parentheses	HINT: `java.util.Stack`(push, peek, pop) + `switch` statement
27	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
28	best-time-to-buy-and-sell-stock
29	Reverse a Linked list

Linked List Insertion:
Linked List Reversal:

30	Remove Linked List elements
31	Move Zeros
32	Max Sub array sum
33	Top k Frequent elements
34	Rotate array to right k steps
35	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;
    }
  };

36	Reverse words in a string
37	Reverse Words
38	Array-1 > unlucky1

References

NeetCode practice