| “Two pointers”, “Sliding window” |
Two Pointers |
Consider using two pointers moving in the same or opposite directions |
Array, String, LinkedList |
| “Subarray”, “Contiguous” |
Sliding Window |
Think about expanding/contracting a window |
Array, HashMap |
| “Tree”, “Binary Tree” |
Tree Traversal |
Consider recursive and iterative approaches; Use DFS or BFS |
Stack, Queue, Recursion |
| “Graph”, “Connected” |
Graph Traversal |
Think about DFS or BFS |
Queue (BFS), Stack/Recursion (DFS) |
| “Sorted array” |
Binary Search, Two Pointers |
Look for opportunities to eliminate half the search space; Use two pointers |
Array |
| “Dynamic Programming”, “Maximum/Minimum” |
DP |
Break problem into subproblems, look for overlapping subproblems |
2D Array, Memoization |
| “Parentheses”, “Valid sequence” |
Stack |
Think about using a stack to match opening/closing elements |
Stack |
| “Top K”, “Kth largest/smallest” |
Heap, QuickSelect |
Consider using a heap to keep track of K elements; Use QuickSelect for O(n) average time |
PriorityQueue/Heap |
| “Intervals”, “Overlapping” |
Interval Manipulation |
Sort intervals, then process |
Array, Sorting |
| “Linked List”, “Cycle” |
Fast & Slow Pointers |
Think about using two pointers moving at different speeds |
LinkedList |
| “Trie”, “Prefix” |
Trie |
Consider building a trie for efficient prefix operations |
Trie |
| “Bit manipulation” |
Bitwise Operations |
Think about using XOR, AND, OR, shift operations |
Integers |
| “Permutation”, “Combination” |
Backtracking |
Consider building a recursive solution with backtracking |
Recursion, Array |
| “Monotonic stack/queue” |
Monotonic Stack |
Think about maintaining a monotonic (increasing/decreasing) stack |
Stack, Queue |
| “Union Find”, “Disjoint Set” |
Union Find |
Consider grouping elements and finding connections |
Array, Tree |
| “In-place operation” |
In-place Algorithms |
Swap corresponding values; Store multiple values in the same pointer |
Array |
| “Common strings” |
Map, Trie |
Use a map for counting; Consider a trie for prefix-based operations |
HashMap, Trie |
| “Recursion banned” |
Iterative Approaches |
Use a stack to simulate recursion |
Stack |
| “General problem” |
Hash Table, Sorting |
Use Map/Set for O(1) time & O(n) space; Sort input for O(nlogn) time and O(1) space |
HashMap, Array |