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Edit File: postfix.js

var Mexp = require('./lexer.js');

Mexp.prototype.toPostfix = function () {
	'use strict';
	var post = [], elem, popped, prep, pre, ele;
	var stack = [{ value: "(", type: 4, pre: 0 }];
	var arr = this.value;
	for (var i = 1; i < arr.length; i++) {
		if (arr[i].type === 1 || arr[i].type === 3 || arr[i].type === 13) {	//if token is number,constant,or n(which is also a special constant in our case)
			if (arr[i].type === 1)
				arr[i].value = Number(arr[i].value);
			post.push(arr[i]);
		}
		else if (arr[i].type === 4) {
			stack.push(arr[i]);
		}
		else if (arr[i].type === 5) {
			while ((popped = stack.pop()).type !== 4) {
				post.push(popped);
			}
		}
		else if (arr[i].type === 11) {
			while ((popped = stack.pop()).type !== 4) {
				post.push(popped);
			}
			stack.push(popped);
		}
		else {
			elem = arr[i];
			pre = elem.pre;
			ele = stack[stack.length - 1];
			prep = ele.pre;
			var flag = ele.value == 'Math.pow' && elem.value == 'Math.pow';
			if (pre > prep) stack.push(elem);
			else {
				while (prep >= pre && !flag || flag && pre < prep) {
					popped = stack.pop();
					ele = stack[stack.length - 1];
					post.push(popped);
					prep = ele.pre;
					flag = elem.value == 'Math.pow' && ele.value == 'Math.pow';
				}
				stack.push(elem);
			}
		}
	}
	return new Mexp(post);
};
module.exports = Mexp;

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