diff --git a/src/hackerrank/implementation/migratoryBirds.ts b/src/hackerrank/implementation/migratoryBirds.ts
index bd7a14fc..0a1467b4 100644
--- a/src/hackerrank/implementation/migratoryBirds.ts
+++ b/src/hackerrank/implementation/migratoryBirds.ts
@@ -17,10 +17,10 @@ function migratoryBirds(arr: number[]): number {
   for (const bird of arr) {
     console.debug(`bird ${bird}`);
 
-    if (!map[bird]) {
-      map[bird] = 1;
-    } else {
+    if (map[bird]) {
       map[bird] += 1;
+    } else {
+      map[bird] = 1;
     }
 
     console.debug(`bird = ${bird} ~> map[bird] = ${map[bird]}`);
diff --git a/src/hackerrank/interview_preparation_kit/dynamic_programming/max_array_sum.ts b/src/hackerrank/interview_preparation_kit/dynamic_programming/max_array_sum.ts
index d6e1c0f3..2a5cffa5 100644
--- a/src/hackerrank/interview_preparation_kit/dynamic_programming/max_array_sum.ts
+++ b/src/hackerrank/interview_preparation_kit/dynamic_programming/max_array_sum.ts
@@ -4,7 +4,11 @@
  */
 
 const bigIntMax = (...args: bigint[]): bigint =>
-  args.reduce((m, e) => (e > m ? e : m), BigInt(0));
+  args.reduce((m, e) => {
+    const _e = BigInt(e);
+    const _m = BigInt(m);
+    return _e > _m ? _e : _m;
+  }, BigInt(0));
 
 function maxSubsetSum(arr: number[]): number {
   const arrCopy: bigint[] = arr.map((x: number): bigint => BigInt(x));
diff --git a/src/hackerrank/interview_preparation_kit/greedy_algorithms/angry_children.ts b/src/hackerrank/interview_preparation_kit/greedy_algorithms/angry_children.ts
index a001ecdb..22e32530 100644
--- a/src/hackerrank/interview_preparation_kit/greedy_algorithms/angry_children.ts
+++ b/src/hackerrank/interview_preparation_kit/greedy_algorithms/angry_children.ts
@@ -7,7 +7,7 @@ function maxMin(k: number, arr: number[]): number {
     .map((x: number): number => x)
     .sort((a: number, b: number): number => a - b);
 
-  let result = sortedlist[sortedlist.length - 1] - sortedlist[0];
+  let result = (sortedlist.at(-1) ?? 0) - sortedlist[0];
 
   for (let i = 0; i < sortedlist.length - k + 1; i++) {
     const tmin = sortedlist[i];
diff --git a/src/hackerrank/interview_preparation_kit/greedy_algorithms/minimum_absolute_difference_in_an_array.ts b/src/hackerrank/interview_preparation_kit/greedy_algorithms/minimum_absolute_difference_in_an_array.ts
index 7d57f51d..7e9074f7 100644
--- a/src/hackerrank/interview_preparation_kit/greedy_algorithms/minimum_absolute_difference_in_an_array.ts
+++ b/src/hackerrank/interview_preparation_kit/greedy_algorithms/minimum_absolute_difference_in_an_array.ts
@@ -7,7 +7,7 @@ function minimumAbsoluteDifference(arr: number[]): number {
     .map((x: number): number => x)
     .sort((a: number, b: number): number => b - a);
 
-  let result = Math.abs(sortedNums[sortedNums.length - 1] - sortedNums[0]);
+  let result = Math.abs((sortedNums.at(-1) ?? 0) - sortedNums[0]);
 
   for (let i = 0; i < sortedNums.length - 1; i++) {
     const aValue = sortedNums[i];
diff --git a/src/hackerrank/interview_preparation_kit/sort/ctci_bubble_sort.ts b/src/hackerrank/interview_preparation_kit/sort/ctci_bubble_sort.ts
index 36f79ff8..6bdb6f9b 100644
--- a/src/hackerrank/interview_preparation_kit/sort/ctci_bubble_sort.ts
+++ b/src/hackerrank/interview_preparation_kit/sort/ctci_bubble_sort.ts
@@ -7,10 +7,9 @@ const SEPARATOR = '\n';
 class SortableGroup {
   group: number[];
 
-  count: number;
+  count = 0;
 
   constructor(group: number[]) {
-    this.count = 0;
     this.group = group;
   }
 
diff --git a/src/hackerrank/interview_preparation_kit/sort/ctci_comparator_sorting.ts b/src/hackerrank/interview_preparation_kit/sort/ctci_comparator_sorting.ts
index cb93559b..6f7ee90f 100644
--- a/src/hackerrank/interview_preparation_kit/sort/ctci_comparator_sorting.ts
+++ b/src/hackerrank/interview_preparation_kit/sort/ctci_comparator_sorting.ts
@@ -53,4 +53,5 @@ export default {
   comparatorSortingPrint
 };
 
-export { Player, SortablePlayer, comparatorSorting, comparatorSortingPrint };
+export { Player } from './ctci_comparator_sorting.Player';
+export { SortablePlayer, comparatorSorting, comparatorSortingPrint };
diff --git a/src/hackerrank/interview_preparation_kit/stacks_and_queues/balanced_brackets.ts b/src/hackerrank/interview_preparation_kit/stacks_and_queues/balanced_brackets.ts
index 877b3ca6..2a1ea30b 100644
--- a/src/hackerrank/interview_preparation_kit/stacks_and_queues/balanced_brackets.ts
+++ b/src/hackerrank/interview_preparation_kit/stacks_and_queues/balanced_brackets.ts
@@ -12,10 +12,7 @@ function isBalancedCompute(s: string): boolean {
   for (const letter of s.split('')) {
     if (letter in pairs) {
       brackets.push(letter);
-    } else if (
-      brackets.length > 0 &&
-      pairs[brackets[brackets.length - 1]] === letter
-    ) {
+    } else if (brackets.length > 0 && pairs[brackets.at(-1) ?? 0] === letter) {
       brackets.pop();
     } else {
       return false;
diff --git a/src/projecteuler/problem0005.ts b/src/projecteuler/problem0005.ts
index adfbbd55..3ffda3b3 100644
--- a/src/projecteuler/problem0005.ts
+++ b/src/projecteuler/problem0005.ts
@@ -33,7 +33,7 @@ function _replaceMaximum(
   const element = _group.get(_element);
 
   if (element) {
-    _group.set(_element, count > element ? count : element);
+    _group.set(_element, Math.max(count, element));
   } else {
     _group.set(_element, count);
   }
diff --git a/src/projecteuler/problem0007.ts b/src/projecteuler/problem0007.ts
index 1f5e0eb8..13011fce 100644
--- a/src/projecteuler/problem0007.ts
+++ b/src/projecteuler/problem0007.ts
@@ -22,7 +22,7 @@ function problem0007(_top: number): number {
 
   console.log(`primes count: ${primes.length}`);
 
-  const answer = primes[primes.length - 1];
+  const answer = primes.at(-1) ?? 0;
 
   const cycles = i;
   console.log(`${_top} prime number is: ${answer} in ${cycles} cycles`);
diff --git a/src/projecteuler/problem0017.ts b/src/projecteuler/problem0017.ts
index 7a4bf0ce..6ff90a43 100644
--- a/src/projecteuler/problem0017.ts
+++ b/src/projecteuler/problem0017.ts
@@ -12,7 +12,7 @@ function problem0017(init: number, last: number): number {
 
   for (let i = init; i <= last; i++) {
     word = numberToWord(i);
-    replaced = word.replace(/[^a-z0-9]/gi, '');
+    replaced = word.replaceAll(/[^a-z0-9]/gi, '');
 
     acum += replaced.length;
 
diff --git a/src/projecteuler/problem0018.ts b/src/projecteuler/problem0018.ts
index 8dc70e8c..c5f690c4 100644
--- a/src/projecteuler/problem0018.ts
+++ b/src/projecteuler/problem0018.ts
@@ -32,7 +32,7 @@ function problem0018(_triangle: number[][]): number {
   console.debug(`leafs: ${leafs.toString()}`);
 
   const __START_FROM__ = 0;
-  const max = leafs.reduce((a, b) => (a > b ? a : b), __START_FROM__);
+  const max = leafs.reduce((a, b) => Math.max(a, b), __START_FROM__);
 
   return max;
 }