solution to this challenge: https://www.reddit.com/r/dailyprogrammer/comments/dv0231/20191111_challenge_381_easy_yahtzee_upper_section/?utm_source=share&utm_medium=web2x

upperSectionScore.js

/**
*
* Given a dice roll result in Yahtzee (input as an array of 5 integers 1-6),
* find the maximum possible score for that roll.
*
* Yahtzee Scoring Rules
* ---------------------
* 1 * numberOfOnes
* 2 * numOFTwos
* 3 * numOfThrees
* 4 * numOfFours
* 5 * numOfFives
* 6 * numOfSixes
*
* Ex. [2, 3, 5, 5, 6] would result in each number being [0, 2, 3, 0, 10, 6],
* and the number to return would be 10
*/
function upperSectionScore(diceResult){
	// handle empty array
	if(diceResult.length === 0){
		return -1;
	}
	// will need a way to count the frequency of each number
	// a variable to store/return the value, and store the largest num freq
	let frequency = {
		'1': 0,
		'2': 0,
		'3': 0,
		'4': 0,
		'5': 0,
		'6': 0
	},
	score = 1;

	// TODO:
	// 1) loop thru each roll, counting the frequency of each number rolled
	// 2) find the largestFreqNum num 
	// 3) using the largestFreqNum, calculate the value and return the score.
	diceResult.reduce((acc, roll, idx) => {
	// 1)
		frequency[roll] += 1;
		let numToCompare = diceResult[idx];
        // 2)
		if(frequency[acc] <= frequency[numToCompare]){
			acc = numToCompare;
		}
        // 3)
		score = acc * frequency[acc];
		return acc;
	}, score);

	return score;
}


console.log(upperSectionScore([2, 3, 5, 5, 6])); // 10
console.log(upperSectionScore([1, 1, 1, 1, 1])); // 5
console.log(upperSectionScore([]));  // -1
console.log(upperSectionScore([2, 4, 3, 4, 4])); // 12
console.log(upperSectionScore([6, 6, 6, 6, 6])); // 30
console.log(upperSectionScore([1, 1, 3, 2, 3])); // 6