#216 - Combination Sum III

Medium • View on LeetCode • View on GitHub

Problem Description

Find all valid combinations of k numbers that sum up to n such that the following conditions are true:

Only numbers 1 through 9 are used.
Each number is used at most once.

Return a list of all possible valid combinations. The list must not contain the same combination twice, and the combinations may be returned in any order.

Solution

/**
 * @param {number} k
 * @param {number} n
 * @return {number[][]}
 */
var combinationSum3 = function(k, n) {
  const result = [];

  function backtrack(history, sum, start) {
    if (sum > n) return;
    if (history.length === k && sum === n) {
      result.push(history);
      return;
    }
    for (let i = start; i < 10; i++) {
      backtrack([...history, i], sum + i, i + 1);
    }
  }

  backtrack([], 0, 1);

  return result;
};