Leetcode Patterns

Pattern recognition accelerates problem-solving. Most interview problems are variations of a small set of underlying patterns. Recognizing the pattern tells you which algorithm to reach for.

Sorted Input

• Apply binary search for efficient lookups
• Use the two-pointer technique for pairs or segments

Unsorted Input

• Dynamic programming for counting ways or optimization problems
• Backtracking for all possibilities and combinations
• Trie for prefix matching
• Hash map / set for quick element lookup
• Monotonic stack or sliding window for continuous max/min values

Graph or Tree Input

• DFS for exploring all paths (when the shortest path is not required)
• BFS for shortest path or fewest steps
• For binary trees, DFS when targeting specific depths or levels

Linked List Input

• Slow/fast pointers or prev / dummy pointers for specific list operations