数奶牛

	// 计算奶牛
	// 初始 1 头奶牛，奶牛在 1 岁和 4 岁的时候生小牛(假设全部为母牛)，5 岁时死亡，求给定的年数奶牛的数量。
	// 以下是我演算的各个方法。
	// 01
	var YEARS = arguments.length > 0 && parseInt(arguments[0], 10) || 10;
	var cows = {},
	cow;
	var _cowIdx = 0,
	_cowNum = 0;
	function addcow() {
	cows[_cowIdx] = {
	'old' : 0,
	'idx': _cowIdx
	};
	_cowNum++;
	_cowIdx++;
	}
	function rmcow(idx) {
	delete cows[idx];
	_cowNum--;
	}
	function proc_cow (cow) {
	cow.old++;
	switch (cow.old) {
	case 1:
	case 4:
	addcow();
	break;
	case 5:
	rmcow(cow.idx);
	break;
	}
	}
	addcow();
	for (var i=0; i<YEARS; i++) {
	for (cow in cows) {
	proc_cow(cows[cow]);
	}
	}
	print(_cowNum);
	// 02
	var YEARS = arguments.length > 0 && parseInt(arguments[0], 10) || 10;
	var cows = {},
	cow;
	var _cowIdx = 0,
	_cowNum = 0;
	function addcow() {
	cows[_cowIdx] = 0;
	_cowNum++;
	_cowIdx++;
	}
	function rmcow(idx) {
	delete cows[idx];
	_cowNum--;
	}
	function proc_cow (cow) {
	switch (++cows[cow]) {
	case 1:
	case 4:
	addcow();
	break;
	case 5:
	rmcow(cow);
	break;
	}
	}
	addcow();
	for (var i=0; i<YEARS; i++) {
	for (cow in cows) {
	proc_cow(cow);
	}
	}
	print(_cowNum);
	// 03
	var YEARS = arguments.length > 0 && parseInt(arguments[0], 10) || 10;
	var cows = {},
	cow;
	var _cowIdx = 0,
	_cowNum = 0;
	cows[++_cowIdx] = 0;
	_cowNum++;
	for (var i=0; i<YEARS; i++) {
	for (cow in cows) {
	switch (++cows[cow]) {
	case 1:
	case 4:
	cows[++_cowIdx] = 0;
	_cowNum++;
	break;
	case 5:
	delete cows[cow];
	_cowNum--;
	break;
	}
	}
	}
	print(_cowNum);
	// 04
	var YEARS = arguments.length > 0 && parseInt(arguments[0], 10) || 10;
	var cows = [0, 0, 0, 0, 0], // 0 - 4 岁奶牛数量
	cow1;
	cows[0] = 1;
	for (var i=0; i<YEARS; i++) {
	cow1 = cows[1];
	cows[1] = cows[0];
	cows[4] = cows[3];
	cows[0] += cows[4];
	cows[3] = cows[2];
	cows[2] = cow1;
	}
	print(cows[4] + cows[3] + cows[2] + cows[1] + cows[0]);
	// 前 3 个是一种思路，最后一个比较吓到我。。。。 :)

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