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---
id: 59e0a8df964e4540d5abe599
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title: Execute Brain****
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challengeType: 5
2019-08-05 16:17:33 +00:00
forumTopicId: 302261
2021-01-13 02:31:00 +00:00
dashedName: execute-brain
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---
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# --description--
Write a function to implement a Brain\*\*\*\* interpreter. The function will take a string as a parameter and should return a string as the output. More details are given below:
RCBF is a set of [Brainf\*\*\* ](https://rosettacode.org/wiki/Brainf*** "Brainf\*\*\*" ) compilers and interpreters written for Rosetta Code in a variety of languages.
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Below are links to each of the versions of RCBF.
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An implementation need only properly implement the following instructions:
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| Command | Description |
| ----------------- | ---------------------------------------------------------------------------------- |
| < code > >< / code > | Move the pointer to the right |
| < code > < < / code > | Move the pointer to the left |
| < code > +< / code > | Increment the memory cell under the pointer |
| < code > -< / code > | Decrement the memory cell under the pointer |
| < code > .< / code > | Output the character signified by the cell at the pointer |
| < code > ,< / code > | Input a character and store it in the cell at the pointer |
| < code > \[</ code > | Jump past the matching < code > ]</ code > if the cell under the pointer is 0 |
| < code > ]</ code > | Jump back to the matching < code > \[</ code > if the cell under the pointer is nonzero |
Any cell size is allowed, EOF (*E*nd-*O*-*F*ile) support is optional, as is whether you have bounded or unbounded memory.
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# --hints--
`brain(bye)` should return a string
```js
assert(typeof brain(bye) === 'string');
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```
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`brain("++++++[>++++++++++<-]>+++++.")` should return "A"
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```js
assert.equal(brain('++++++[>++++++++++< - ] > +++++.'), 'A');
```
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`brain(bye)` should return `Goodbye, World!\r\n`
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```js
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assert.equal(brain(bye), 'Goodbye, World!\r\n');
```
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`brain(hello)` should return `Hello World!\n`
```js
assert.equal(brain(hello), 'Hello World!\n');
```
`brain(fib)` should return `1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89`
```js
assert.equal(brain(fib), '1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89');
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```
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# --seed--
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## --before-user-code--
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```js
let fib=`+
++
+++
++++
+>+>>
>>++++
+++++++
++++++++
+++++++++
++++++++++
++++++>++++
++++++++++++
+++++++++++++
+++< < < < < < [>[>>
>>>>+>+< < < < < < < -
]>>>>>>>[< < < < < < <
+>>>>>>>-]< [>++++
++++++[-< - [ > >+>+< <
< - ] > >>[< < < +>>>-]+< [
>[-]< [-]]>[< < [>>>+< <
< - ] > >[-]]< < ]>>>[>>+>+
< < < - ] > >>[< < < +>>>-]+< [>
[-]< [-]]>[< < +>>[-]]< < < <
< < < ]>>>>>[++++++++++++++
+++++++++++++++++++++++++
+++++++++.[-]]++++++++++< [
->-< ]>+++++++++++++++++++++
+++++++++++++++++++++++++++.
[-]< < < < < < < < < < < < [>>>+>+< < < < - ] >
>>>[< < < < +>>>>-]< - [ > >.>.< < < [-]]
< < [>>+>+< < < - ] > >>[< < < +>>>-]< < [< +
>-]>[< +>-]< < < - ] ` ;
let hello='++++++++[>++++[>++>+++>+++>+< < < < - ] > +>+>->>+[< ]< - ] > >.>---.+++++++..+++.>>.< -. < . + + + . ------ . -------- . > >+.>++.'
let bye='++++++++++[>+>+++>++++>+++++++>++++++++>+++++++++>++++++++++>+++++++++++>++++++++++++< < < < < < < < < - ] > >>>+.>>>>+..< . < + + + + + + + + . > >>+.< < +.< < < < ++++.< ++.>>>+++++++.>>>.+++.< +++++++.--------.< < < < < +.< +++.---.';
```
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## --seed-contents--
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```js
function brain(prog) {
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}
```
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# --solutions--
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```js
function brain(prog){
var output="";
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var code; // formatted code
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var ip = 0; // current instruction within code
var nest = 0; // current bracket nesting (for Out button)
var ahead = []; // locations of matching brackets
var data = [0]; // data array (mod by +, -)
var dp = 0; // index into data (mod by < , >)
var inp = 0; // current input character (fetch with ,)
var quit = 0;
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var commands = {
'>':function() { if (++dp >= data.length) data[dp]=0 },
'< ':function() { if (--dp < 0 ) quit + + } ,
'+':function() { ++data[dp] },
'-':function() { --data[dp] },
'[':function() { if (!data[dp]) ip = ahead[ip]; else ++nest },
']':function() { if ( data[dp]) ip = ahead[ip]; else --nest },
',':function() {
var c = document.getElementById("input").value.charCodeAt(inp++);
data[dp] = isNaN(c) ? 0 : c; // EOF: other options are -1 or no change
},
'.':function() {
output+=String.fromCharCode(data[dp]);
/*var s = document.getElementById("output").innerHTML)
+ String.fromCharCode(data[dp]);
s = s.replace(/\n/g,"< br > ").replace(/ /g,"& nbsp;");
document.getElementById("output").innerHTML = s;*/
},
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};
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let ar=prog.split('');
var st = [], back, error = -1;
for (ip=0; ip< ar.length ; ip + + ) {
switch(ar[ip]) {
case '[':
st.push(ip);
break;
case ']':
if (st.length == 0) error = ip;
back = st.pop();
ahead[ip] = back;
ahead[back] = ip;
break;
}
}
for(ip=0;ip< ar.length ; ip + + ) {
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if(commands.hasOwnProperty(ar[ip]))
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commands[ar[ip]]();
}
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return output;
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}
```