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Leetcode tips

 If input array is sorted then

    - Binary search
    - Two pointers

If asked for all permutations/subsets then
    - Backtracking

If given a tree then
    - DFS
    - BFS

If given a graph then
    - DFS
    - BFS

If given a linked list then
    - Two pointers

If recursion is banned then
    - Stack

If must solve in-place then
    - Swap corresponding values
    - Store one or more different values in the same pointer

If asked for maximum/minumum subarray/subset/options then
    - Dynamic programming

If asked for top/least K items then
    - Heap

If asked for common strings then
    - Map
    - Trie

Else
    - Map/Set for O(1) time & O(n) space
    - Sort input for O(nlogn) time and O(1) space

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