index.js

const transactionsArray = require('./transactions'); /* importing transactions from a different file */

const simplifyDebts = (transactions) => {

	const entities = ['paidBy', 'paidFor'];

	let targets = {}; /* targets is the object that stores entities and their values.
						Values can be positive signalling debt and negative signalling credit { 'A' : 100 } */
	let data = [];

	transactions.forEach(transaction => {

		let payingEntity = transaction[entities[0]];
		let paidForEntites = Object.keys(transaction[entities[1]]); /* convert the keys into an array to make iterable */
		if(paidForEntites.length == 1) {
			let paidBy = { 'paidBy': paidForEntites[0] };
			let paidFor = {'paidFor' : { [payingEntity] : transaction[entities[1]][paidForEntites[0]] } };
	
			data.push(paidBy,paidFor);
			return;
		}

		paidForEntites.forEach(paidEntity => {

			if (targets[paidEntity])
				targets[paidEntity] += transaction[entities[1]][paidEntity]; /* if entity exists , add value */

			else
				targets[paidEntity] = 0 + transaction[entities[1]][paidEntity];


			if (targets[transaction[entities[0]]])
				targets[transaction[entities[0]]] -= transaction[entities[1]][paidEntity];

			else
				targets[transaction[entities[0]]] = 0 - transaction[entities[1]][paidEntity];
		});

	})


	let sortedArray = [];
	for (var target in targets) {
		sortedArray.push([target, targets[target]]);  /* [ [ 'B', 0 ],[ 'F', 622 ]]	   */
	}

	while (sortedArray.filter((element) => !Boolean(element[1])).length != sortedArray.length) { /* loop runs till values of all the elements changes to 0 */


		let paidFor = {};
		let paidBy = {};

		sortedArray.sort((a, b) => b[1] - a[1]); /* sort array to decreasing */

		if (sortedArray[0][1] > -sortedArray[sortedArray.length - 1][1]) { /* if debt is greater than credit */

			// paidBy[sortedArray[0][0]] = -sortedArray[sortedArray.length - 1][1]; /* add entry to the transaction { paidBy : { 'A' : 50 } } */

			paidBy = { 'paidBy': sortedArray[0][0] }; // so a number that that is -ive is found which is not greater than the max element

			paidFor[sortedArray[sortedArray.length - 1][0]] = -sortedArray[sortedArray.length - 1][1]; /* { paidFor: { A: 1204 } } */

			sortedArray[0][1] += sortedArray[sortedArray.length - 1][1];
			sortedArray[sortedArray.length - 1][1] = 0;

			data.push(paidBy, { paidFor });
		} else {


			paidBy = { 'paidBy': sortedArray[0][0] }; // so a number that that is -ive is found which is not greater than the max element

			paidFor[sortedArray[sortedArray.length - 1][0]] = sortedArray[0][1];
			sortedArray[sortedArray.length - 1][1] += sortedArray[0][1];
			sortedArray[0][1] = 0;

			data.push(paidBy, { paidFor });
		}
	}
	console.log(data);
}

simplifyDebts(transactionsArray);