The single-digit case is fine, you just check pi[i] == i and move on.
Clarify the problem constraints and edge cases, then propose an efficient algorithm that iterates through possible starting indices, computes the length of the index, and checks if the substring matches the index as a string. Discuss time and space complexity, and consider optimizations like early termination or precomputation if needed.
Pro tip: Demonstrate awareness of edge cases such as indices near the end of the string where the substring might be shorter than the index length, and mention that the solution should handle large inputs efficiently by avoiding unnecessary substring creations.
Restate the problem in your own words and confirm details like 1-based indexing, the definition of 'length equal to the number of digits in i', and that the substring must exactly match the decimal representation of i.
Consider the length of pi's digits (could be large), indices near the end where the substring might be out of bounds, and indices with varying digit lengths (e.g., 1-digit, 2-digit, etc.).
Iterate over possible starting indices i from 1 to n, compute the number of digits d of i, check if i+d-1 <= n, and compare the substring of length d starting at i-1 (0-based) with the string representation of i. Collect matches.
Discuss time complexity O(n * d) where d is the average number of digits, and space complexity O(1) excluding output. Mention potential optimizations like avoiding substring creation by comparing characters directly.
Walk through a small example (e.g., pi digits '31415926') to verify the algorithm, and test edge cases like no matches or matches at the very end.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.