Mathematics

Number theory, combinatorics, geometry and arithmetic puzzles.

83 problems

Title	Tags	Acceptance	Difficulty
1. Climbing Stairs	Dynamic Programming · Recursion	—	Easy
2. Sum of Digits	Math	—	Easy
3. GCD and LCM	Math · Number Theory	—	Easy
4. Is It Prime?	Math · Primes	—	Easy
5. Count Primes	Sieve of Eratosthenes	—	Medium
6. Factorial Trailing Zeros	Math	—	Easy
7. Pascal's Triangle	Math · Array	—	Easy
8. nCr Modulo 1e9+7	Combinatorics · Modular Arithmetic	—	Medium
9. Missing Number	Math · Bit Manipulation	—	Easy
10. Factorial	Math · Big Integer	—	Easy
11. N-th Fibonacci Modulo	Fast Doubling · Matrix Power	—	Medium
12. Primes up to N	Sieve	—	Easy
13. Prime Factorisation	Factorisation	—	Easy
14. Number of Divisors	Divisors	—	Easy
15. Sum of Divisors	Divisors	—	Easy
16. Perfect Number	Divisors	—	Easy
17. Armstrong Number	Digits	—	Easy
18. Reverse an Integer	Digits	—	Easy
19. Palindrome Number	Digits	—	Easy
20. Digital Root	Digits · Modular Arithmetic	—	Easy
21. LCM of an Array	GCD · LCM	—	Easy
22. Modular Exponentiation	Fast Power	—	Medium
23. Modular Inverse	Extended Euclid · Fermat	—	Medium
24. Combinations nCr	Combinatorics	—	Easy
25. Catalan Number	Combinatorics	—	Medium
26. Digits of N!	Logarithms	—	Medium
27. Collatz Steps	Simulation	—	Easy
28. Decimal to Any Base	Number Bases	—	Easy
29. Any Base to Decimal	Number Bases	—	Easy
30. GCD of an Array	GCD	—	Easy
31. Euler's Totient	Totient	—	Medium
32. Sum of Two Squares	Two Pointers · Math	—	Medium
33. Goldbach Pair	Primes	—	Medium
34. Primes in a Range	Sieve · Prefix Sum	—	Medium
35. Pythagorean Triplets	Brute Force	—	Medium
36. Power of Two	Bits	—	Easy
37. Happy Number	Cycle Detection	—	Easy
38. N-th Ugly Number	Dynamic Programming	—	Medium
39. Excel Column Title	Number Bases	—	Easy
40. Excel Column Number	Number Bases	—	Easy
41. Integer Square Root	Binary Search	—	Easy
42. Integer K-th Root	Binary Search	—	Medium
43. Sum of All Digits 1..N	Digit DP	—	Hard
44. Sum of Squares 1..N	Formula	—	Easy
45. Leap Years in a Range	Inclusion–Exclusion	—	Easy
46. Clock Angle	Geometry	—	Easy
47. Triangle Type	Geometry	—	Easy
48. Polygon Area	Geometry · Shoelace	—	Medium
49. Points in Rectangle	Geometry	—	Easy
50. Count Set Bits	Bits	—	Easy
51. Set Bits for 0..N	Bits · DP	—	Easy
52. The Single Number	XOR	—	Easy
53. Single Number Among Triples	Bits	—	Medium
54. Reverse Bits	Bits	—	Easy
55. Hamming Distance	XOR	—	Easy
56. Total Hamming Distance	Bits · Counting	—	Medium
57. Find the Duplicate Number	XOR · Cycle Detection	—	Medium
58. Sum of All Subset XORs	Bits · Combinatorics	—	Medium
59. Bitwise AND of a Range	Bits	—	Medium
60. Power of Four	Bits	—	Easy
61. Maximum XOR of Two Numbers	Trie · Bits	—	Hard
62. Bits to Flip	XOR	—	Easy
63. Two Numbers with Odd Counts	XOR	—	Medium
64. Loan EMI	Formula	—	Medium
65. Day of the Week	Calendar · Zeller	—	Medium
66. Days Between Dates	Calendar	—	Medium
67. Minimum Moves to Equal Elements	Math	—	Medium
68. Minimum Moves to Equal Elements II	Median	—	Medium
69. Minimum Cost to Move Chips	Parity	—	Easy
70. Steps to Reduce a Number to Zero	Simulation · Bit Manipulation	—	Easy
71. Water Bottles	Simulation	—	Easy
72. Bulb Switcher	Math	—	Medium
73. Broken Calculator	Greedy	—	Medium
74. Integer Replacement	Greedy · Bit Manipulation	—	Medium
75. Valid Perfect Square	Binary Search	—	Easy
76. Arranging Coins	Math · Binary Search	—	Easy
77. Power of Three	Math	—	Easy
78. Maximum 69 Number	Greedy	—	Easy
79. Self-Dividing Numbers	Math	—	Easy
80. N-th Tribonacci Number	DP	—	Easy
81. Count Odd Numbers in a Range	Math	—	Easy
82. Product Minus Sum of Digits	Math	—	Easy
83. Nim Game	Game Theory	—	Easy

83 of 83 problems