#259 Combination Target Sum

Given an array of distinct integers nums and a target integer target, return all unique combinations of numbers from nums that sum to target.

Rules:

• Each number can be used unlimited times
• All numbers in nums are distinct
• Order of numbers within a combination doesn't matter
• Order of combinations in the result doesn't matter

Constraints:

• 1 ≤ nums.length ≤ 20
• 2 ≤ nums[i] ≤ 30
• 2 ≤ target ≤ 30
• All elements in nums are distinct

Examples:

// Example 1:

console.log(combinationSum([2,5,6,9], 9));
// Output: [[2,2,5], [9]]

// Explanation: 

// 2 + 2 + 5 = 9

// 9 = 9


// Example 2:

console.log(combinationSum([3,4,5], 16));
// Output: [[3,3,3,3,4], [3,3,5,5], [4,4,4,4], [3,4,4,5]]


// Example 3:

console.log(combinationSum([3], 5));
// Output: []

// Explanation: No combinations sum to 5