Use a single-pass scan over the byte array, decoding the leading byte to determine the expected number of continuation bytes, then verify each continuation byte starts with '10'. Handle edge cases like truncated sequences and invalid leading bytes (e.g., 0xFF) explicitly.
Pro tip: Clarify that this is a classic state-machine problem and that you can solve it in O(n) time and O(1) space; mention that the same logic applies to streaming data, which is relevant for ML pipelines processing text.
Confirm the input format (list of integers 0-255) and that the sequence must be a complete, valid UTF-8 encoding. Ask about edge cases like empty input or overlong encodings.
Identify the valid leading byte ranges: 0xxxxxxx (1 byte), 110xxxxx (2 bytes), 1110xxxx (3 bytes), 11110xxx (4 bytes). Continuation bytes must match 10xxxxxx.
Iterate through the array; for each leading byte, compute the number of expected continuation bytes and verify the next bytes are valid continuations. If any check fails, return false.
Ensure the sequence doesn't end mid-character, and reject bytes like 0xFF or 0xFE that are never valid in UTF-8. Also consider overlong encodings if the problem requires strict validation.
State that the algorithm runs in O(n) time and O(1) space. Walk through a few test cases: valid multi-byte character, invalid continuation, truncated sequence.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Clarify that battleships are 1×k or k×1 rectangles, separated by at least one water cell, and that no extra memory means O(1) auxiliary space. Then propose a single-pass scan where a ship is counted only at its top-left cell (i.e., when the current cell is 'X' and neither the cell above nor the cell to the left is 'X').
Pro tip: Explicitly state that you're counting only the top-left cell of each ship to avoid double-counting, and mention that this works because ships are straight and non-adjacent. This shows you understand the invariant and can reason about correctness without extra memory.
Confirm that battleships are 1×k or k×1 rectangles, separated by at least one water cell, and that 'no extra memory' means O(1) auxiliary space (the board itself can be modified or not).
Recognize that each ship has exactly one top-left cell (the cell with no 'X' above or to the left). Counting only these cells yields the number of ships.
Iterate over every cell; if board[i][j] == 'X' and (i == 0 or board[i-1][j] != 'X') and (j == 0 or board[i][j-1] != 'X'), increment the count.
State O(m*n) time and O(1) extra space. Discuss edge cases: empty board, single cell, ships touching borders, and ships of length 1.
Relate the problem to efficient in-place processing of large matrices (e.g., feature maps or adjacency grids) where memory is constrained, emphasizing the importance of O(1) auxiliary space.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.