Greedy

LeetCode 763 note: record each letter’s last index, extend the current part’s end while scanning, and cut when the scan reaches it

LeetCode 452 note: sort by end and shoot at the end; only a balloon starting after the arrow needs a new one, and touching ends count as overlapping

LeetCode 4099 note: the swaps needed equal the inversion count; every locked position some element must cross has to be unlocked, so count those, compare with k, and add the inversions counted with merge sort

LeetCode 4098 note: value’s smallest prime factor p decides everything: the next element is at least value + p, then even numbers step by 2; the left side is feasible iff value - p >= 2 * index

Parsing nested structures, simulations that interact with the previous element, monotonic stacks, greedy deletion for the smallest string, and a lazy-deletion Max Stack

heapq basics, Top-K, lazy deletion, two heaps, k-way merge, sweep line, and Dijkstra

Sort then scan, intervals sorted by right end, left and right passes, pairing and parity invariants, adjacent differences, and “remove what exceeds the average”, each with why greedy is correct

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 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 1354 note: work backwards, since the maximum was set last; jump with a modulo when the gap is large

LeetCode 420 note: three length cases; when too long, delete from runs with len % 3 == 0 first to cancel replacements

LeetCode 2193 note: greedily fix the outer pair: take the last character and swap its leftmost partner to the front, costing that index; the unpaired character ends in the middle, costing its distance there