#techniques
4 articles
Prefix Sums
Precompute running totals so any range sum becomes one subtraction. The prefix sum technique turns O(n) per query into O(1) — and the hashmap combo unlocks a whole class of subarray counting problems.
Monotonic Stacks
The monotonic stack is the O(n) trick for finding the next greater or smaller element — a sorted stack you maintain on the fly, with one deceptively simple pop-while loop at its core. Used in Daily Temperatures, Largest Rectangle in Histogram, and Trapping Rain Water.
Greedy Algorithms
Make the locally optimal choice and never look back — when greedy is correct it beats dynamic programming cold. The hard part isn't the algorithm, it's knowing when greed works and when it quietly hands you the wrong answer.
Binary Search (Beyond the Sorted Array)
Master the binary search algorithm once and for all — the invariant that kills off-by-one bugs, and the "search on the answer" trick that works on problems that don't look like binary search at all.