<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(),'/');
} function calCard(stack,cards,oper)
{
if (stack.length < 2)
{
return;
}
steps.push(oper);
calcul(stack,oper);
playCards(stack, cards);
steps.pop(oper);
} function Play()
{
var stack = new Array();
var cards = new Array();
Result.value = "";
ResultSet.length = 0;
for (var i = 0; i < iCards.length; i++)
{
if (iCards[i].value == "" || isNaN(iCards[i].value))
{
alert('输入格式不正确');
iCards[i].focus();
return false;
}
cards.push(iCards[i].value);
}
playCards(stack, cards);
Result.value += ResultSet.toString();
}
</script>
<body>
<br/>
<input id = 'iCards' style='width:80px'/>
<input id = 'iCards' style='width:80px'/>
<input id = 'iCards' style='width:80px'/>
<input id = 'iCards' style='width:80px'/>
<input type='button' value='计算' onclick="Play();"/><br/><br/>
计算结果:<br/>
<textarea id = 'Result' style='width:440px;height:200px'></textarea>
</body>
</html> 
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