203 lines
5.1 KiB
Markdown
203 lines
5.1 KiB
Markdown
---
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id: 59e0a8df964e4540d5abe599
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title: Execute Brain****
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challengeType: 5
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forumTopicId: 302261
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dashedName: execute-brain
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---
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# --description--
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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:
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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 |
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| ------------------------- | ------------------------------------------------------------------------------------------ |
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| <code>></code> | Move the pointer to the right |
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| <code><</code> | Move the pointer to the left |
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| <code>+</code> | Increment the memory cell under the pointer |
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| <code>-</code> | Decrement the memory cell under the pointer |
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| <code>.</code> | Output the character signified by the cell at the pointer |
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| <code>,</code> | Input a character and store it in the cell at the pointer |
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| <code>\[</code> | Jump past the matching <code>]</code> if the cell under the pointer is 0 |
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| <code>]</code> | Jump back to the matching <code>\[</code> if the cell under the pointer is nonzero |
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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--
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`brain(bye)` should return a string
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```js
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assert(typeof brain(bye) === 'string');
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```
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`brain("++++++[>++++++++++<-]>+++++.")` should return "A"
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```js
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assert.equal(brain('++++++[>++++++++++<-]>+++++.'), 'A');
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```
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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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```
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`brain(hello)` should return `Hello World!\n`
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```js
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assert.equal(brain(hello), 'Hello World!\n');
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```
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`brain(fib)` should return `1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89`
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```js
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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
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let fib=`+
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++
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+++
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++++
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+>+>>
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>>++++
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+++++++
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++++++++
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+++++++++
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++++++++++
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++++++>++++
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++++++++++++
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+++++++++++++
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+++<<<<<<[>[>>
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>>>>+>+<<<<<<<-
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]>>>>>>>[<<<<<<<
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+>>>>>>>-]<[>++++
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++++++[-<-[>>+>+<<
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<-]>>>[<<<+>>>-]+<[
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>[-]<[-]]>[<<[>>>+<<
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<-]>>[-]]<<]>>>[>>+>+
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<<<-]>>>[<<<+>>>-]+<[>
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[-]<[-]]>[<<+>>[-]]<<<<
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<<<]>>>>>[++++++++++++++
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+++++++++++++++++++++++++
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+++++++++.[-]]++++++++++<[
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->-<]>+++++++++++++++++++++
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+++++++++++++++++++++++++++.
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[-]<<<<<<<<<<<<[>>>+>+<<<<-]>
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>>>[<<<<+>>>>-]<-[>>.>.<<<[-]]
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<<[>>+>+<<<-]>>>[<<<+>>>-]<<[<+
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>-]>[<+>-]<<<-]`;
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let hello='++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.'
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let bye='++++++++++[>+>+++>++++>+++++++>++++++++>+++++++++>++++++++++>+++++++++++>++++++++++++<<<<<<<<<-]>>>>+.>>>>+..<.<++++++++.>>>+.<<+.<<<<++++.<++.>>>+++++++.>>>.+++.<+++++++.--------.<<<<<+.<+++.---.';
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```
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## --seed-contents--
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```js
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function brain(prog) {
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}
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```
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# --solutions--
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```js
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function brain(prog){
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var output="";
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var code; // formatted code
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var ip = 0; // current instruction within code
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var nest = 0; // current bracket nesting (for Out button)
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var ahead = []; // locations of matching brackets
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var data = [0]; // data array (mod by +, -)
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var dp = 0; // index into data (mod by <, >)
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var inp = 0; // current input character (fetch with ,)
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var quit = 0;
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var commands = {
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'>':function() { if (++dp >= data.length) data[dp]=0 },
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'<':function() { if (--dp < 0) quit++ },
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'+':function() { ++data[dp] },
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'-':function() { --data[dp] },
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'[':function() { if (!data[dp]) ip = ahead[ip]; else ++nest },
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']':function() { if ( data[dp]) ip = ahead[ip]; else --nest },
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',':function() {
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var c = document.getElementById("input").value.charCodeAt(inp++);
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data[dp] = isNaN(c) ? 0 : c; // EOF: other options are -1 or no change
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},
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'.':function() {
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output+=String.fromCharCode(data[dp]);
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/*var s = document.getElementById("output").innerHTML)
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+ String.fromCharCode(data[dp]);
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s = s.replace(/\n/g,"<br>").replace(/ /g,"&nbsp;");
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document.getElementById("output").innerHTML = s;*/
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},
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};
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let ar=prog.split('');
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var st = [], back, error = -1;
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for (ip=0; ip<ar.length; ip++) {
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switch(ar[ip]) {
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case '[':
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st.push(ip);
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break;
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case ']':
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if (st.length == 0) error = ip;
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back = st.pop();
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ahead[ip] = back;
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ahead[back] = ip;
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break;
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}
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}
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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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}
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return output;
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}
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```
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