answers to problems

answers

//Copy this over the contents at tddbin.com
//Replace the [] in the assert statements with a functional equivalant
//Reference here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
//Lambda syntax: (x,y) => x + y, works in firefox, try it out :)
 
function range(start, end, jump) {
	jump = jump || 1
	if (start && !end)
	return actualRange(0, start, jump)
	return actualRange(start, end, jump)
}
 
function actualRange(start, end, jump) {
	var result = []
	for (var i = start; i < end; i += jump)
		result.push(i)
	return result
}
 
describe('For loops vs Map/Filter/Reduce', function() {
 
		it('creates the same list', function() {
				var numbers = [];
				for (var i = 0; i < 100; i++){
				numbers.push(i * 2)
				}
				assert.deepEqual(numbers, range(0,100).map(x => x*2)); 
				});
 
		it('creates the same list', function() {
				var people = ['james', 'jane', 'anne'];
				var peopleStartingWithJ = [];
				for (var i = 0; i < people.length; i++) {
				  if (people[i][0] === 'j')
				    peopleStartingWithJ.push(people[i])
				}
				assert.deepEqual(peopleStartingWithJ,
				  people.filter(name => name[0]==='j'))
				});
 
		it('creates the same list', function() {
				var people = ['james', 'jane', 'anne'];
				var firstLetterOfName = [];
				for (var i = 0; i < people.length; i++) {
				firstLetterOfName.push(people[i][0])
				}
				assert.deepEqual(firstLetterOfName, people.map(name => name[0]))
				});
 
		it('creates the same list', function() {
				var people = [5, 10, 15]
				var sum = 0
				for (var i = 0; i < people.length; i++) {
				sum += people[i]
				}
				assert.equal(sum, people.reduce((acc, x)=>acc+x,0))
				});
 
		it('creates the same list', function() {
				var people = [11, 10, 15]
				var allLargerThan10 = true;
				for (var i = 0; i < people.length; i++) {
				if (people[i] <= 10) {
				allLargerThan10 = false;
				break;
				}
				}
				assert.deepEqual(allLargerThan10, people.reduce((acc,x) => acc ? (x <= 10) : acc, true))
				});
 
		it('creates the same list', function() {
				var people = [5, 10, 15]
				var anyLargerThan10 = false;
				for (var i = 0; i < people.length; i++) {
				if (people[i] > 10) {
				anyLargerThan10 = true;
				break;
				}
				}
				assert.deepEqual(anyLargerThan10, people.reduce((acc, x) => acc ? acc : (x > 10), false))
				});
 
		//Reduce Challenges
		//Note: I'm not encouraging using reduce everywhere, this is just an exercise
		it('solves this using reduce', function() {
				var people = ['james', 'jane', 'anne'];
				var firstLetterOfName = [];
				for (var i = 0; i < people.length; i++) {
				firstLetterOfName.push(people[i][0])
				}
				assert.deepEqual(firstLetterOfName, 
				  people.reduce((acc, x)=>acc.concat([x[0]]), []))
				});
 
		it('solves this using reduce', function() {
				var people = ['james', 'jane', 'anne'];
				var peopleStartingWithJ = [];
				for (var i = 0; i < people.length; i++) {
				if (people[i][0] === 'j')
				peopleStartingWithJ.push(people[i])
				}
				assert.deepEqual(peopleStartingWithJ, 
				  people.reduce((acc, x) => x[0] === 'j' ? acc.concat([x]) : acc , []))
				});
  //Nesting
		it('returns the indices of two product prices that add up to credit', function() {
				var credit = 100;
				var productPrices = [5, 75, 25]
				var productIndicies = [0,0];
				for (var i = 0; i < productPrices.length; i++)
				  for (var j = i + 1; j < productPrices.length; j++)
				    if (productPrices[i] + productPrices[j] === credit)
				      productIndicies = [i,j]
 
        // array [first pos] of arrays [second pos] of arrays [pos1, pos2, sum]
        var sums = productPrices.map(
            (val, index) => productPrices.slice(index+1).map((x, index2)=>[index, index + index2 + 1, x+val]));
        // flatten
        var candidates = sums.reduce((acc, x) => acc.concat(x), []);
        // dropWhile better but not available here...
        var matches = candidates.filter(candidate => candidate[2] === credit);
				assert.deepEqual(productIndicies, matches[0].slice(0,2))
				});
});