A comprehensive guide to 16 fundamental DSA patterns that provide a structured approach to solving coding problems. Covers sliding window, two pointers, fast/slow pointers, prefix sum, binary search, heaps, bit manipulation, dynamic programming, backtracking, DFS/BFS, union find, topological sort, greedy algorithms, stacks, tries, and Kadane's algorithm. Each pattern includes when to use it, how it works with examples, and why it's effective, emphasizing pattern recognition over memorizing individual problems.