77. Combinations

Problem

Tags: Backtracking

Given two integers n and k, return all possible combinations of k numbers out of the range [1, n].

You may return the answer in any order.

Example 1:

Input: n = 4, k = 2
Output:
[
  [2,4],
  [3,4],
  [2,3],
  [1,2],
  [1,3],
  [1,4],
]

Example 2:

Input: n = 1, k = 1
Output: [[1]]

Constraints:

• 1 <= n <= 20
• 1 <= k <= n

Code

JS

// 77. Combinations (4/9/53740)
// Runtime: 116 ms (77.30%) Memory: 44.04 MB (94.84%) 

/**
 * @param {number} n
 * @param {number} k
 * @return {number[][]}
 */
function combine(n, k) {
    const result = [];
    backtrack(1, []);
    return result;

    function backtrack(start, curr) {
        if (curr.length === k) return result.push([...curr]);
        for (let i = start; i <= n; i++) {
            curr.push(i);
            backtrack(i + 1, curr);
            curr.pop();
        }
    }
}