collatz.js

// Every number can be reduced to 1 applying the following rules:
// If the number is even divide by two (halve it)
// If the number is odd multiply by 3 and add 1
// Students were asked to find the largest "chain" from numbers 2 to 100. 
// Answer is 97 (118) as shown by the following script, then 73 (115), then 54/55 (112).
// Exercise was done as a whole class.

var collatz = function(minNum, maxNum) {
	var links = '', temp, steps;
	for ( var i = minNum; i <= maxNum; i++ ) {
		temp = i;
		if ( temp > 1 ) {
			steps = 1;
			links = temp + " -> ";
			while ( temp > 1 ) {
				if ( temp % 2 === 0 ) {
					temp = temp / 2;
				} else {
					temp = (3 * temp) + 1;
				}
				if ( temp > 1 ) {
					links += temp + " -> ";
					steps++;
				}
			}
		}
		console.log(links + "1" + "   (" + (steps || "0") + ")");
		console.log(" ");
	}
};