Leetcode Problem 77. Combinations

77. Combinations

Leetcode Solutions

Initialize an empty list ans to store the final combinations.
Define a recursive function backtrack that takes the current combination curr and the next starting number firstNum.
If the length of curr is k, add a copy of curr to ans and return.
Calculate the number of elements still needed to reach a combination of length k (need = k - curr.length).
Calculate the number of elements remaining in the range [firstNum, n] (remain = n - firstNum + 1).
Calculate the number of elements available to be added to curr (available = remain - need).
Iterate over the range [firstNum, firstNum + available] and for each number: a. Add the number to curr. b. Recursively call backtrack with the updated curr and num + 1 as the new firstNum. c. Remove the last number from curr to backtrack.
Start the backtracking process by calling backtrack with an empty curr and firstNum = 1.
Return ans.

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