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LeetCode 739 — asked at Amazon, Google, and Meta. Find the number of days until a warmer temperature using a monotonic decreasing stack. Store indices not temperatures, pop when current day is warmer, and solve six related problems with the same O(n) pattern.
LeetCode 128 — asked at Google, Amazon, and Meta. Find the longest consecutive integer sequence in O(n) using a HashSet. Only start counting from numbers where num-1 is absent — each element is visited at most twice total, making an apparent O(n²) nested loop amortized O(n).
LeetCode 763 — asked at Amazon, Google, and Meta. Partition a string into the maximum number of pieces so each letter appears in exactly one piece. Map each character to its last occurrence, then greedily extend the current partition boundary — O(n) time, O(1) space.
LeetCode 621 — asked at Google, Meta, and Amazon. Schedule tasks with a cooldown n to minimize total time. Use the greedy formula max(len(tasks), (max_count - 1) * (n + 1) + count_of_max) or simulate with a max-heap and queue — both O(tasks) time.
LeetCode 452 — asked at Amazon, Google, and Microsoft. Find the minimum number of arrows to burst all balloons by sorting by end coordinate and greedily shooting through overlapping intervals. O(n log n) time, O(1) space — the classic greedy interval scheduling pattern.