Count PrimesCount the number of prime numbers less than a non-negative number, n. 提示 解題應用 HashTable Array Math 規律觀查 Default:123func countPrimes(n int) int {} 解答思路:非常典型的空間換取時間，因為
Happy NumberWrite an algorithm to determine if a number is “happy”. A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of t
Single NumberGiven an array of integers, every element appears twice except for one. Find that single one. Note: Your algorithm should have a linear runtime complexity. Could you implement it without
Valid SudokuThe Sudoku board could be partially filled, where empty cells are filled with the character ‘.’. Note: A valid Sudoku board (partially filled) is not necessarily solvable. Only the fille