FreeCodeCamp - Pairwise

pairwise.js

function pairwise(arr, arg) {
	// hold the indexes that add up to arg
	var indexes = [];

	// iterate over each element in the original array
	arr.forEach(function (curVal, index, array) {
		var outerIndex = index;

		// compare to each element in the original array
		array.forEach(function (val, indx, ar) {
			var innerIndex = indx;

			// if you are comparing the same index of the original array
			// then don't take any action
			if (outerIndex === innerIndex) {
				// do nothing
			}

			// if the values adds up:
			else if (curVal + val === arg) {
				// pus the indexes of the values to the indexes array if that index is not already there
				if (indexes.indexOf(outerIndex) === -1) {
					indexes.push(outerIndex);
				}

				if (indexes.indexOf(innerIndex) === -1) {
					indexes.push(innerIndex);
				}
			}
		});
	});

	// sum up the values
	return indexes.reduce(function(previousValue, currentValue) {
		return previousValue + currentValue;

	}, 0);
}