Easy

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 884 note: count words across both sentences together; those appearing exactly once are the answer

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 876 note: fast moves two steps and slow one; when fast reaches the end slow is in the middle, the right-middle for even lengths

LeetCode 872 note: collect leaves left to right with DFS; BFS collects level by level, which is not left-to-right order

LeetCode 868 note: remember the last 1’s position and take the maximum distance at each new 1

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 859 note: lengths must match; identical strings need a repeated character; otherwise exactly two positions differ and cross-match

LeetCode 844 note: simulate backspaces with a stack; for O(1) space, walk from the end and count how many characters each # skips

LeetCode 836 note: two rectangles overlap exactly when their x intervals and y intervals both overlap, i.e. min(right) > max(left)

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