Multiply and surrender

longestCommonSubstring.js

//helper function
String.prototype.cut = function(index){
	return this.slice(0, index) + this.slice(index+1);
}

function longestCommonSubstring(a, b){
	if(a.length == 0 || b.length == 0)
		return 0;
	
	if(a == b)
		return a.length;
	
	let longest = 0;
	for(let i = 0; i < a.length; i++)
		longest = Math.max(longest, longestCommonSubstring(a.cut(i), b));
	for(let i = 0; i < b.length; i++)
		longest = Math.max(longest, longestCommonSubstring(a, b.cut(i)));
	
	return longest;
}