adventofcalendarday1.js

// blackjack sum
// given a goal sum and a list of integers, find pairs that add up to the goal
// return their product
// worse-case quadratic, for each in the list, I check all possibilities from the bottom up

// start at the highest number, scan up from the bottom, as soon as I break my goal I exit
let goal = 2020
let bottomup = [1721, 979, 366, 299, 675, 1456].sort((a,b) => a - b) // sort from the largest to the smallest
let topdown = bottomup.slice().reverse()

outer:
for(var j = topdown.length; j > 0; --j){
    inner:
    for(var k = 0; k < bottomup.length; k++){
        if(topdown[j] + bottomup[k] > goal){
            // if we overshoot, break out of the inner increment and move onto the next value from "topdown"
            break inner
        }
        if(topdown[j] + bottomup[k] === goal){
            // if we get a match, break out of the whole program
            console.log(`${topdown[j]} * ${bottomup[k]} = ${topdown[j] * bottomup[k]}`)
            // 299 * 1721 = 514579
            break outer
        }
            // otherwise, no sum found, move onto the next one down
    }
}