puzzle2a.js

const input = require('./input/puzzle2a_input.json');

function count_letters(string, minimum_count){
    return new Promise(function(resolve, reject){
        const letter_count = {};
        //loop through and count each occurence of each letter and save it in an object
        for (let i = 0; i < string.length; i++) {
            const element = string[i];
            if (element in letter_count) {
                letter_count[element]++;
            } else {
                letter_count[element] = 1;
            }
        }
        // see if any of the letters have a count equal to the minimum_count param
        // a separate for loop is used because you don't want to count false positives.
        for(let key in letter_count){
            const letter = letter_count[key];
        
            if (letter == minimum_count) {
                // call promise resolve method to exit the loop and return the boolean.
                resolve(true);
            }
        };

        resolve(false);
    });
}

function get_checksum(input){
    return new Promise((resolve, reject)=>{
        const twos = [];
        const threes = [];
        // set up all the count_letter promises
        for (let i = 0; i < input.length; i++) {
            const string = input[i];
            twos.push(count_letters(string, 2))
            threes.push(count_letters(string, 3));
        }

        Promise.all(twos).then((two_vals)=>{
            // when all the 2 letter promises return count how many trues you have
            let two_count = 0
            for (let t = 0; t < two_vals.length; t++) {
                if(two_vals[t]){
                    two_count++;
                }
            }
            console.log(two_count);
            Promise.all(threes).then((three_vals)=>{
                // when all the 3 letter promises return count how many trues you have
                let three_count= 0
                for (let t = 0; t < three_vals.length; t++) {
                    if(three_vals[t]){
                        three_count++;
                    }
                }
                console.log(three_count);
                // we have all the counts therefore resolve with the checksum
                resolve(two_count * three_count);
            });
        }).catch((err)=>{
            console.log(err);
        });
        
    });

}

get_checksum(input).then((res)=>{
    console.log("Checksum: ", res)
});