combinationSum.js

/*
39. Combination Sum
Given an array of distinct integers candidates and a target integer target, 
return a list of all unique combinations of candidates where the chosen numbers sum to target. 
You may return the combinations in any order.

The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the 
frequency of at least one of the chosen numbers is different.

The test cases are generated such that the number of unique combinations that sum up to target is 
less than 150 combinations for the given input.

Example 1:
Input: candidates = [2,3,6,7], target = 7
Output: [[2,2,3],[7]]
Explanation:
2 and 3 are candidates, and 2 + 2 + 3 = 7. Note that 2 can be used multiple times.
7 is a candidate, and 7 = 7.
These are the only two combinations.

Example 2:
Input: candidates = [2,3,5], target = 8
Output: [[2,2,2,2],[2,3,3],[3,5]]

Example 3:
Input: candidates = [2], target = 1
Output: []
*/

/**
 * @param {number[]} candidates
 * @param {number} target
 * @return {number[][]}
 */
var combinationSum = function (candidates, target) {
    let result = []

    let iterate = (index, sum, temp) => {
        if (sum > target) return
        if (sum == target) {
            result.push(temp)
            return
        }
        for (let i = index; i < candidates.length; i++) {
            if (candidates[i] > target) continue
            iterate(i, sum + candidates[i], [...temp, candidates[i]])
        }
    }
    iterate(0, 0, [])
    return result
};

// Using Backtracking

var combinationSum = function (candidates, target) {
    // global result
    const result = []
    candidates.sort((a, b) => a - b)

    // dfs recursive helper
    const dfs = (i, candidates, target, slate) => {
        // backtracking case
        if (target < 0) return

        // base case
        if (target === 0) {
            result.push(slate.slice())
            return
        }

        // dfs recursive case
        for (let j = i; j < candidates.length; j++) {
            slate.push(candidates[j])
            dfs(j, candidates, target - candidates[j], slate)
            slate.pop()
        }
    }
    dfs(0, candidates, target, [])
    return result
}

console.log(combinationSum([2, 3, 5], 8))