Journal Archive

2022

/**
 * @param {number} k
 * @param {number} n
 * @return {number[][]}
 */
var combinationSum3 = function(k, n) {
	// simple cases
    let min = k * (k + 1) / 2;
    let max = 45; // sum 1 to 9;
    
    if (n < min || n > max) return [];
    

    let result = [];
    // helper function to backtrack
    const findCombination = (arr, target, index) => {
        if (arr.length === k && target === n) {
            result.push(arr);
            return;
        }
        if (arr.length < k && target < n) {
            for (let i = index; i <= 9; i++) {
                findCombination([...arr, i], target + i, i + 1);
            }
        }
        
    }
    
    findCombination([], 0, 1);
    
    return result;
    
    
};

Day 48: Solving one of LeetCode problems

216. Combination Sum III Difficulty - Medium

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.

 

Example 1:

Input: k = 3, n = 7
		Output: [[1,2,4]]
Explanation:
1 + 2 + 4 = 7
There are no other valid combinations.

Example 2:

Input: k = 3, n = 9
Output: [[1,2,6],[1,3,5],[2,3,4]]
Explanation:
1 + 2 + 6 = 9
1 + 3 + 5 = 9
2 + 3 + 4 = 9
There are no other valid combinations.

Example 3:

Input: k = 4, n = 1
Output: []
Explanation: There are no valid combinations.
Using 4 different numbers in the range [1,9], the smallest sum we can get is 1+2+3+4 = 10 and since 10 > 1, there are no valid combination.