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function balance(str,a,b) {
var g = 0;
for (var i = 0; i < str.length; i++) {
var f = str.charAt(i);
if (f==a)
g++;
else if (f==b) {
g--;
if (g<0)
return false;
}
}
return g==0;
}
var str = "(a+5)*((5.67+b)*甲+乙)";
alert(
balance(str,"(",")") && /^(\(*([a-z]+|[\u4e00-\u9fa5]+|\d+(\.\d{1,2})?)\)*([\+\-\*\/](?!$)|$))+$/i.test(str)
);