我学习JavaScript才一个月,我正在尝试实现Shunting Yard Algorithm
然而,我似乎在某个地方(可能在while循环中)有一个逻辑错误,但我一生都搞不清楚。
var parser = function(inp){
var outQueue=[];
var opStack=[];
Array.prototype.peek = function() {
return this.slice(-1)[0];
};
//tokenize
var inArr=tokenize(inp);
var top;
var prec = {
"^" : "right",
"*" : "left",
"/" : "left",
"+" : "left",
"-" : "left"
};
var assoc = {
"^" : 4,
"*" : 3,
"/" : 3,
"+" : 2,
"-" : 2
};
inArr.forEach(function(v) {
//If the token is a number, then push it to the output queue
if(v.match(/\d+/)) {
outQueue.push(v);
}
//If the token is an operator, o1, then:
else if(v.match(/[+*-/^]/)) {
if (opStack.peek()) {
top = opStack.peek();
//while there is an operator token o2, at the top of the operator stack and
while(top.match(/[+*-/^]/)
//either o1 is left-associative and its precedence is less than or equal to that of o2,
&& ((assoc[v]==="left" && prec[v] <= prec[top])
//or o1 is right associative, and has precedence less than that of o2,
|| (assoc[v]==="right" && prec[v] < prec[top]))) {
outQueue.push(opStack.pop());
top = opStack.peek();
}
}
//at the end of iteration push o1 onto the operator stack
opStack.push(v);
}
//If the token is a function token, then push it onto the stack.
else if(v.match(/(sin|cos|tan)/)) {
opStack.push(v);
}
//If the token is a function argument separator
else if(v===",") {
//Until the token at the top of the stack is a left parenthesis
//pop operators off the stack onto the output queue.
while(opStack.peek() != "(") {
outQueue.push(opStack.pop());
}
/*if(opStack.length == 0){
console.log("Mismatched parentheses");
return;
}*/
}
//If the token is a left parenthesis (i.e. "("), then push it onto the stack.
else if(v==="(") {
opStack.push(v);
}
//If the token is a right parenthesis (i.e. ")"):
else if(v===")") {
//Until the token at the top of the stack is a left parenthesis, pop operators off the stack onto the output queue.
while(opStack.peek() != "(") {
outQueue.push(opStack.pop());
}
/*if(opStack.length == 0){
console.log("Unmatched parentheses");
return;
}*/
//Pop the left parenthesis from the stack, but not onto the output queue.
opStack.pop();
//If the token at the top of the stack is a function token, pop it onto the output queue.
if(opStack.peek().match(/(sin|cos|tan)/)) {
outQueue.push(opStack.pop());
}
}
});
return outQueue.concat(opStack.reverse()).join(" ");
};
function tokenize(arg) {
return arg.split(" ");
}
console.log(parser("5 + 3 * 6 - ( 5 / 3 ) + 7"));
正确输出:
5 3 6 * + 5 3 / - 7 +
实际产量:
5 3 6 5 3 / 7 + - * +
[请原谅我的格式,我在移动电话上]
最佳答案
你混淆了两个变量
在检查优先级的部分:
&& ((assoc[v]==="left" && prec[v] <= prec[top])
//or o1 is right associative, and has precedence less than that of o2,
|| (assoc[v]==="right" && prec[v]
检查assoc[v]是否已离开。assoc只保存数字,所以这总是错误的。将
assoc
s更改为prec
,反之亦然。