Knapsack with dynamic programming

knapsack

var testInput = [
	[1, 1],
	[3, 4],
	[4, 5],
	[5, 7]
];

var knapsackOpt = function (arr) {
	var matrix = [];
	// Loop over the given elements
	for (let i = 0; i < arr.length; i++) {
		matrix[i] = [];
		// For each element, loop from 0 to the value of the heaviest item
		for (let j = 0; j <= arr[arr.length - 1][1]; j++) { 
			// For each of these iteration check what the best we can do is
			var option1;
			if (arr[i][0] === j) {
				option1 = arr[i][1];
			} else if (arr[i][0] > j) {
				option1 = 0;
			} else {
				// The base that we can afford
				option1 = arr[i][1];
				// Calculate how much space we have left
				var rest = j - arr[i][0];
				option1 += matrix[i - 1] && matrix[i - 1][rest] ? matrix[i - 1][rest] : 0;
			}
			// Find out what option2 is
			var option2 = matrix[i - 1] && matrix[i - 1][j] ? matrix[i - 1][j] : 0;
			// Write the bigger of the two options to the matrix
			matrix[i][j] = Math.max(option1, option2);
		}
	}
	// Return the very last element in the matrix
	return matrix[matrix.length - 1][matrix[matrix.length - 1].length - 1];
};

// Tests
var testRes = knapsackOpt(testInput);
console.log('expect output of testInput to be 9 ', testRes === 9);