Given an integer n, return true if and only if it is an Armstrong number. The k-digit number n is an Armstrong number if and only if the kth power of each digit sums to n. Example 1: Input: n = 153 Output: true Explanation: 153 is a 3-digit number, and 153 = 13 + 53 + 33. Example 2: Input: n = 123 Output: false Explanation: 123 is a 3-digit number, and 123 != 13 + 23 + 33 = 36. Constraints: 1 <= n <= 108