Solutions to https://blog.svpino.com/2015/05/07/five-programming-problems-every-software-engineer-should-be-able-to-solve-in-less-than-1-hour

fiveproblems.js

// Problem 1
function forSum(arr) {
	var sum = 0, i;
	for(i = 0; i < arr.length; arr++) {
		sum += arr[i];
	}
	return sum
}
function whileSum(arr) {
	var sum = 0, i = arr.length;
	while (i--) sum += arr[i];
	return sum
}
function recSum(arr, i) {
	i = i === undefined ? 0 : i;
	return arr[i] + recSum(arr, i + 1);
}

// Problem 2
function joinArr(a1, a2) {
	if(a1.length !== a2.length) throw 'Arrays must be same length';
	var na = [];
	for(var i = 0; i < a1.length; i++) {
		na.push(a1[i]);
		na.push(a2[i]);
	}
	return na;
}

// Problem 3
function fib(n) {
	var a = 0, 
		b = 1, 
		z = 0,
		fiba = [];
	for(var i = 0; i < n; i ++) {
		fiba.push(a);
		z = a;
		a += b;
		b = z;
	}
	return fiba;
}

// Problem 4
function biggestPossibleNumber(arr) {
	return parseInt(arr
		.map(function(c) { return c.toString(); })
		.sort().reverse()
		.reduce(function(p, c) { return p + "" + c; }));
}

// Problem 5
function sumTo100() {
	var v = ['1', '2', '3', '4', '5', '6', '7', '8', '9'],
		ops = ['', '-', '+'],
		i = 0; //Bitmask, 00 00 00 00 00 00 00 00
		// Each bit pair, in dec, is the index of the op between n and n+1
		// 00 - ''
		// 01 - '-'
		// 10 - '+'
		// 11 - skip somehow?
	function pad(s) {
		while(s.length < 8) {
			s = "0" + s;
		}
		return s;
	}
	function op(bitmask, pair) {
		val = pad(bitmask.toString(3))[pair];
		return ops[val];
	}

	while(i.toString(3).length <= 8) {
		//We still have combos to try
		// 1 o1 2 .. o8 9
		var calc = '';
		for(var h = 0; h < 8; h++) {
			calc += v[h] + op(i, h);
		}
		calc += v[8];
		if(eval(calc) === 100) console.log(calc);
		i++;
	}
}
sumTo100()