adventofcalendarday1_c.js

// Find the complement to each highest number and search the lower numbers for the complement
// So it could be recursive, given a sorted array, loop through it from the top down, handing the lower half of the list to yourself

// base case: I have 2 numbers to fill. 
let goal = 2020
let list = [1721, 979, 366, 299, 675, 1456]

let [a,b] = findsum(list, goal, 2)
console.log(a, b, a + b, a * b)
// 1721 299 2020 514579
let [x,y,z] = findsum(list, goal, 3)
console.log(x,y,z,x+y+z, x*y*z)
// 979 366 675 2020 241861950

function findsum(all, target, n){
  if(n > 2){
      for(var each of all){
          let complement = target - each
          let result = findsum(all.slice(0,-1), complement, n - 1)
          if(result){
              return [].concat(each, result)
          } // otherwise try the next one
      } // if we run out of things to try return undefined
  } else { // I do have two
        let marbles = new Set(all)
        for(var marble of marbles){
            let complement = target - marble
            if(marbles.has(complement)){
                return [marble, complement]
            } // else try the next marble
        } // if I don't find any solutions I return undefined and the function caller knows I couldn't find anything
    }
}

// basically I'm finding the complementary list -- hand down a list of how many numbers I need, and what they need to equal