Evaluates well-formed reverse polish notation expressions (http://en.wikipedia.org/wiki/Reverse_Polish_notation).
Strings with tokens separated by single spaces. Tokens are operators or operands. Operators are +, -, * or /. Operands are integers or floats (e.g. 7, 3.23, -1e9).
The value of the evaluated expression.
"1 1 +" -> 2
"5 8 -" -> -3
"2 3 7 + -" -> -8
"5 3 * 5 +" -> 20
| function(a, // The input string | |
| b) { // Placeholder var that will become the stack | |
| return (b = [])[ // Create an empty stack, and later return its 0th element (*) | |
| a.replace(/\S+/g, // For each token (everything that does not | |
| // contain spaces) in the string, | |
| function(c) { // inspect and act on it: | |
| b.push( // Something will always be pushed to the stack: | |
| +c || // If it is a number (an operand), push the number itself. | |
| eval( // Else it is an operator. | |
| b.pop(a = b.pop()) + // Pop the topmost element and save it in a. | |
| // Then pop the next element and | |
| c + // apply the operator together with the | |
| a)) // previously saved element. | |
| }), | |
| 0] // (*) After going through all tokens, index the 0th element | |
| // of the stack. This is the result of the expression. | |
| } |
| function(a,b){return(b=[])[a.replace(/\S+/g,function(c){b.push(+c==c?c:eval(b.pop(a=b.pop())+c+a))}),0]} |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| Version 2, December 2004 | |
| Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE> | |
| Everyone is permitted to copy and distribute verbatim or modified | |
| copies of this license document, and changing it is allowed as long | |
| as the name is changed. | |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION | |
| 0. You just DO WHAT THE FUCK YOU WANT TO. |
| { | |
| "name": "rpn", | |
| "description": "Reverse Polish Notation expression evaluator", | |
| "keywords": [ | |
| "expression", | |
| "parser", | |
| "rpn", | |
| "evaluator" | |
| ] | |
| } |
| <!DOCTYPE html> | |
| <title>RPN</title> | |
| <div>Expected value: <b>3, -4, -8, 14</b></div> | |
| <div>Actual value: <b id="ret"></b></div> | |
| <script> | |
| // write a small example that shows off the API for your example | |
| // and tests it in one fell swoop. | |
| var myFunction = function(a,b){return(b=[])[a.replace(/\S+/g,function(c){b.push(+c==c?c:eval(b.pop(a=b.pop())+c+a))}),0]} | |
| document.getElementById( "ret" ).innerHTML = [myFunction('1 2 +'), myFunction('2 6 -'), myFunction('2 3 7 + -'), myFunction('5 1 2 + 4 * + 3 -')].join(', '); | |
| </script> |
Save 2 bytes.
function(a,b){return(b=[])[a.replace(/\S+/g,function(c,d){b.push(+c==c?+c:{'+':(d=b.pop(a=b.pop()))+a,'-':d-a,'*':d*a,'/':d/a}[c])}),0]}
or this
function(a,b){return(b=[])[a.replace(/\S+/g,function(c,d){b.push(+c==c?+c:[(d=b.pop(a=b.pop()))+a,d-a,d*a,d/a]['+-*/'.indexOf(c)])}),0]}
I'm learning something in every comment. Great work, @tsaniel!
With ES6 you can
d variable to the top so you can ignore one (, )=> function you can also remove all return and make one liner by omitting {} that makes it return the first thing(a,b,d)=>(b=[])[a.replace(/\S+/g,c=>b.push(+c==c?+c:{'+':(d=b.pop(a=b.pop()))+a,'-':d-a,'*':d*a,'/':d/a}[c])),0]
Using the ideas outlined above, the eval-less version now is under 140 bytes too (138 bytes):
function(a,b){return(b=[])[a.replace(/\S+/g,function(c,d){b.push(+c==c?+c:(d=b.pop(a=b.pop()),c=='+'?d+a:c=='-'?d-a:c=='*'?d*a:d/a))}),0]}Thanks everyone.