Classic BFS/DFS problem and I knew it the second I read it.
Treat the grid as a graph and use DFS or BFS to explore each unvisited land cell, marking all connected land as visited to count one island. Iterate through every cell, incrementing the island count each time you start a traversal from an unvisited '1'.
Pro tip: Mention that you can optimize space by mutating the grid in-place (e.g., changing '1' to '0') if allowed, but always clarify with the interviewer first. Also, discuss handling very large grids with BFS to avoid recursion depth limits.
Restate the problem to ensure understanding: count connected components of '1's using 4-directional adjacency. Ask about constraints (e.g., grid size, mutability) and edge cases (empty grid, all water).
Decide between DFS (recursive or iterative) and BFS. Explain trade-offs: DFS is simpler but may hit recursion limits; BFS uses a queue and is safer for large grids.
Iterate over each cell. When encountering an unvisited '1', increment island count and launch a traversal to mark all connected land cells as visited (e.g., set to '0' or use a visited matrix).
State time complexity O(m*n) since each cell is visited once, and space complexity O(m*n) in worst case for recursion stack or queue, or O(1) if mutating grid in-place.
Walk through a small example (e.g., 3x3 with one island) and edge cases (no islands, all land, single row/column) to verify correctness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
This one looked easy for about thirty seconds.
Recognize that the target word 'GOOGLE' has specific character counts: G:2, O:2, L:1, E:1. For each character, count its occurrences in the array, then multiply the combinations of choosing the required number of each character from its available count. Since indices are distinct, use binomial coefficients for each character and multiply them together.
Pro tip: Clarify that the order of selection doesn't matter and that each index is distinct, so we're counting combinations, not permutations. Also, mention that if any character count is insufficient, the answer is zero.
Restate the problem: count subsets of indices whose characters can be rearranged to form 'GOOGLE'. Note that rearrangement means we only need the correct multiset of characters.
Count the frequency of each character in 'GOOGLE': G appears 2 times, O 2 times, L 1 time, E 1 time. All other characters are irrelevant.
Iterate through the given array and count how many times each of the required characters (G, O, L, E) appears.
For each required character, if the available count is less than the needed count, the answer is 0. Otherwise, compute the binomial coefficient C(available, needed) for that character.
Multiply the binomial coefficients for all required characters to get the total number of ways. Return the product.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.