Array

LeetCode 747 note: find the largest and second largest in one pass and return the largest’s index if it is at least twice the second; multiply to avoid dividing by zero

LeetCode 744 note: find the first letter > target (an upper bound), wrapping around to the first letter if none exists

LeetCode 733 note: DFS or BFS from the start, recoloring 4-directional cells that share the start’s original color; return immediately if the colors are equal

LeetCode 705 note: a fixed number of buckets, with the key modulo the bucket count choosing the bucket and a list per bucket handling collisions

LeetCode 704 note: a closed interval [l, r] with an integer mid; return on a match, otherwise discard the half that cannot contain the target

LeetCode 697 note: record each value’s count, first index and last index; among the most frequent values, take the shortest span

LeetCode 682 note: keep valid scores on a stack; C removes the last, D adds its double, and + adds the sum of the last two

LeetCode 674 note: one pass that extends the run while strictly increasing and resets to 1 otherwise, updating the maximum after the loop too

LeetCode 661 note: each cell becomes the floored average of the existing cells in its 3 × 3 neighborhood, written into a new matrix

LeetCode 645 note: use sums: missing = sum of 1..n - sum of the set, duplicate = array sum - sum of the set

LeetCode 628 note: after sorting there are only two candidates: the three largest, or the two smallest (negatives) times the largest

LeetCode 605 note: scan left to right and plant in any empty plot whose neighbors are empty; a new flower blocks the next plot, so actually update the array