LeetCode

LeetCode 4045 note: merge robots already close at t = 0, then go right to left like car fleets, where anything faster than the fleet ahead eventually joins it

LeetCode 3313 note: the last marked node is the farthest one, and a farthest node can always be a diameter endpoint

LeetCode 2608 note: BFS from every node; a visited neighbor that is not the parent closes a cycle of length dist[u] + dist[v] + 1

LeetCode 2561 note: every value’s total must be even; sort the excess, and each cheap half item swaps with an expensive one at min(its value, 2 × global minimum)

LeetCode 716 note: store unique ids on both the stack and the heap, record deletions by id, and discard deleted entries lazily; tracking values cannot tell duplicates apart

LeetCode 622 note: a fixed array plus head and count, every position taken modulo the capacity, and count deciding empty versus full

LeetCode 2218 note: piles are taken from the top, so taking x coins is worth a prefix sum; a grouped knapsack with dp[j] = the best value taking j coins so far, enumerating how many from each pile

LeetCode 4019 note: kept characters never change again, so record each character’s last position in the result; a new character within k of it gets merged away

LeetCode 2416 note: each Trie node counts the words passing through it, and a word’s answer is the sum of counts along its path

LeetCode 987 note: collect (col, row, val) triples, sort them, and group by column

LeetCode 940 note: group by last character; distinct subsequences ending with c = every current distinct subsequence with c appended, plus c itself, replacing the old value

LeetCode 2973 note: the max product of three is either the three largest or the two smallest times the largest, so each subtree returns only its 2 smallest and 3 largest values, merged in post-order