LeetCode

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

LeetCode 824 note: split into words and convert each: move a leading consonant to the end, then append ma and i + 1 copies of a

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