Medium

LeetCode 3843 note: count each value, then count how many values share each count; the first element from the left whose count is its own is the answer

LeetCode 3840 note: houses conflict only when adjacent with the same color; take a house outright when the colors differ, and do the House Robber choice only when they match

LeetCode 3839 note: words sharing the first k characters are connected, so count by word[:k]; exclude words shorter than k

LeetCode 3719 note: n is only 1500, so fix the left end and extend right, maintaining distinct odds and evens in two sets

LeetCode 2838 note: sort monsters by power, build coin prefix sums, and bisect_right per hero

LeetCode 1570 note: store only non-zero (index, value) pairs, and compute the dot product by merging the two index-sorted lists with two pointers, multiplying only on equal indices

LeetCode 1229 note: sort both people’s slots, then find intersections with two pointers as in 986; the first intersection that is long enough is the earliest slot

LeetCode 3835 note: cost = (max - min) × length only grows as the window grows, so a sliding window counts subarrays; two monotonic deques keep the window’s max and min

LeetCode 3834 note: a stack simulation where a new element merges with an equal top, possibly again with the new top

LeetCode 2054 note: with at most two events, pair each event with the most valuable event that ends before it starts; sort by end time and use a prefix max with binary search

LeetCode 244 note: precompute each word’s positions (sorted by construction), then answer each query by merging the two position lists with two pointers, always advancing the smaller one

LeetCode 986 note: two pointers each hold an interval, the intersection is [max(starts), min(ends)], and the interval that ends first cannot meet anything else, so its pointer advances