<html>
<head>
</head>
<script language='javascript'>
var debug = false;
var steps = new array();
var resultset = new array();
resultset.add = function(newresult)
{
for (var i = 0; i < resultset.length; i++)
{
if (resultset[i] == newresult)
{
return;
}
}
resultset.push(newresult);
}
resultset.tostring = function()
{
var msg = "";
for (var i = 0; i < resultset.length; i++)
{
msg += resultset[i] + "=24\n";
}
msg += "计算结束，共得到"+resultset.length+"个不同结果";
return msg;
}
function assert(flag)
{
if (!flag)
{
throw new error('assertion failed!');
}
}
array.prototype.clone = function()
{
return this.slice(0);
}
function calcul(stack,oper)
{
assert(oper == '+' || oper == '-' || oper == '*' || oper == '/');
var lift = new array();
lift[0] = stack.pop()-0;
lift[1] = stack.pop()-0;
switch(oper)
{
case '+': stack.push(lift[1] + lift[0]);
break;
case '-': stack.push(lift[1] - lift[0]);
break;
case '*': stack.push(lift[1] * lift[0]);
break;
case '/': stack.push(lift[1] / lift[0]);
break;
}
return lift;
}
function parseexp() //由逆波兰式构造出表达式
{
var stack = new array();
var exprs = new array();
for (var i = 0; i < steps.length; i++)
{
if (!isnan(steps[i]))
{
stack.push(steps[i]);
exprs.push(steps[i].tostring());
}
else
{
var oper1 = exprs.pop();
var oper2 = exprs.pop();
var lift = calcul(stack, steps[i]);
if (steps[i] == '*' || steps[i] == '+') //规定较大的数出现在*和+的左边，以避免出现过多重复的结果
{
if (lift[0] > lift[1])
{
var tmp = oper1;
oper1 = oper2;
oper2 = tmp;
}
}
var subexpr = "(" + oper2 + ")" + steps[i] + "(" + oper1 + ")"; //判断是否要添加括号
var subexpr1 = oper2 + steps[i] + oper1;
var subexpr2 = "(" + oper2 + ")" + steps[i] + oper1;
var subexpr3 = oper2 + steps[i] + "(" + oper1 + ")";
if (math.abs(eval(subexpr) - eval(subexpr1)) < 0.0001) subexpr = subexpr1;
else if (math.abs(eval(subexpr) - eval(subexpr2)) < 0.0001) subexpr = subexpr2;
else if (math.abs(eval(subexpr) - eval(subexpr3)) < 0.0001) subexpr = subexpr3;
exprs.push(subexpr);
}
}
return exprs[0];
}
function playcards(stack, cards)
{
if (debug) alert(stack + ":" + cards);
if (stack.length == 1 && cards.length == 0)
{
if(math.abs(stack[0] - 24) < 0.0001)
{
resultset.add(parseexp());
}
return; //计算结束，输出计算结果
}
var newcards = null;
var newstack = null;
for(var i = 0 ; i < cards.length; i++)
{
var distinctcard = true;
for (var j = 0; j < i; j++)
{
if (cards[j] == cards[i])
{
distinctcard = false;
break;
}
}
if (distinctcard)
{
newcards = cards.clone();
newstack = stack.clone();
newcards.splice(i,1);
newstack.push(cards[i]);
steps.push(cards[i]);
playcards(newstack, newcards);
steps.pop(cards[i]);
}
}
calcard(stack.clone(),cards.clone(),'+');
calcard(stack.clone(),cards.clone(),'-');
calcard(stack.clone(),cards.clone(),'*');
calcard(stack.clone(),cards.clone(),'/');
}
