Source: https://leetcode.com/problems/combination-sum-ii/

Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations.

/**
* @param {number[]} candidates
* @param {number} target
* @return {number[][]}
*/
// O(2^N) time, O(N) space
var combinationSum2 = function(candidates, target) {
 // Sort the numbers first to get rid of duplicates
 candidates.sort();
 
 const combinations = [];
 
 const combinationSumHelper = (startIndex, currentCombo, remaining) => {
   if (remaining < 0) {
     return;
   }
   // We found a combination that adds up to the target
   if (remaining === 0) {
     combinations.push([...currentCombo]);
     return;
   }
   
   for (let i = startIndex; i < candidates.length; i++) {
     // Skip duplicate numbers
     if (i > startIndex && candidates[i] === candidates[i-1]) {
       continue;
     }
     
     const currentNum = candidates[i];
     currentCombo.push(currentNum);
     
     combinationSumHelper(i + 1, currentCombo, remaining - currentNum);
     
     currentCombo.pop();
   }
 };
 
 combinationSumHelper(0, [], target);
 return combinations;
};