Generate all subsets (power set) of a list of numbers.
Given digits 2-9, return all possible letter combinations (phone keypad).
Return all permutations of a list of distinct integers.
Given n and k, return all combinations of k numbers from 1 to n.
Find all unique combinations that sum to target. Numbers can be reused.
Place 4 queens on 4x4 board with no two threatening each other.
Does a word exist in a 2D grid? Move up/down/left/right, no cell reuse.
Partition a string so every substring is a palindrome. Return all partitions.
Generate all combinations of n pairs of well-formed parentheses.