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Leetcode
Medium
Backtracking
Combinatorics
Recursion
Google
Combinations

Generate all size-k combinations of numbers from 1 to n.

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LeetCode Combinations

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Problem Statement

Given two integers n and k, return all possible combinations of k distinct numbers chosen from the range 1 to n.

Each combination should contain numbers in increasing order, and the collection of combinations may be returned in any order.

Input Format

  • Two integers n and k.
  • The valid numbers are 1, 2, ..., n.
  • Choose exactly k distinct numbers.

Output Format

  • Return a list of all combinations.
  • Each combination is a list of k integers in strictly increasing order.
  • The order of combinations in the final answer does not matter.

Constraints

  • 1 <= k <= n
  • 1 <= n
  • The number of combinations can be large, so all valid results should be generated explicitly.
Examples
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Example 1

Input

n = 4, k = 2

Output

[[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]

Explanation

Choose any 2 distinct numbers from 1 through 4. Each valid pair appears once.

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