memoizer.js

//JavaScript : The Good Parts
//闭包，存储数据
var memoizer = function (memo, formula) {
	var recur = function(n){
		var result = memo[n];
		if (typeof result !== 'number') {
			result = formula(recur, n);
			memo[n] = result;
		};
		return result;
	}
	return recur;
};
//费波纳契数列
var fibonacci = memoizer([0,1], function(recur, n){
	return recur(n - 1) + recur(n -2);
});
//阶乘
var factorial = memoizer([1,1], function(recur, n){
	return n * recur(n - 1);
});