Array

LeetCode 888 note: equal sums after swapping x and y means y = x + (sumB - sumA) / 2; put B in a set and check each x from A

LeetCode 883 note: the top view counts nonzero cells, and the front and side views sum each row’s and each column’s maximum

LeetCode 867 note: the transpose is n × m with res[j][i] = matrix[i][j]; in Python, zip(*matrix)

LeetCode 860 note: track only the counts of $5 and $10 bills; for $15 change prefer 10 + 5, since $5 bills are more versatile

LeetCode 832 note: reverse each row and invert its bits, which two pointers can do at once

LeetCode 821 note: one left-to-right pass for the distance to the nearest c on the left, then a right-to-left pass taking the minimum

LeetCode 819 note: replace punctuation with spaces, lowercase, split, count, and pick the most frequent word not banned

LeetCode 812 note: with at most 50 points, enumerate every triple and take the largest shoelace area

LeetCode 806 note: simulate writing, wrapping when the next letter would exceed 100; landing exactly on 100 stays on the line

LeetCode 804 note: translate each word into a Morse string and count the distinct results with a set

LeetCode 766 note: every diagonal is constant exactly when each cell equals its upper-left neighbor

LeetCode 748 note: count the plate’s letters in lowercase, then find the shortest word covering every count, taking the earliest on ties