Given an array arr that represents a permutation of numbers from 1 to n. You have a binary string of size n that initially has all its bits set to zero. At each step i (assuming both the binary string and arr are 1-indexed) from 1 to n, the bit at position arr[i] is set to 1. You are given an integer m and you need to find the latest step at which there exists a group of ones of length m. A group of ones is a contiguous substring of 1s such that it cannot be extended in either direction. Return the latest step at which there exists a group of ones of length exactly m. If no such group exists, return -1. Example 1: Input: arr = [3,5,1,2,4], m = 1 Output: 4 Explanation: Step 1: "00100", groups: ["1"] Step 2: "00101", groups: ["1", "1"] Step 3: "10101", groups: ["1", "1", "1"] Step 4: "11101", groups: ["111", "1"] Step 5: "11111", groups: ["11111"] The latest step at which there exists a group of size 1 is step 4. Example 2: Input: arr = [3,1,5,4,2], m = 2 Output: -1 Explanation: Step 1: "00100", groups: ["1"] Step 2: "10100", groups: ["1", "1"] Step 3: "10101", groups: ["1", "1", "1"] Step 4: "10111", groups: ["1", "111"] Step 5: "11111", groups: ["11111"] No group of size 2 exists during any step. Example 3: Input: arr = [1], m = 1 Output: 1 Example 4: Input: arr = [2,1], m = 2 Output: 2 Constraints: n == arr.length 1 <= n <= 10^5 1 <= arr[i] <= n All integers in arr are distinct. 1 <= m <= arr.length