Trouble with parsing a string into a tree in JS

Question

This code converts string into an array tree, but does so with a bug -

// I have this input
const input = "(1 (2 (4 5 6 (7) 108 (9)) 3))";

// and this function


class TreeNode {
  constructor(value) {
    this.value = value;
    this.children = [];
  }
}


function parseInput(input) {
  let root = null;
  let current = null;
  const stack = [];

  for (let i = 0; i < input.length; i++) {
    const char = input[i];

    if (char === '(') {
      if (current !== null) {
        const newNode = new TreeNode(current);
        if (stack.length > 0) {
          stack[stack.length - 1].children.push(newNode);
        } else {
          root = newNode;
        }
        stack.push(newNode);
        current = null;
      }
    } else if (char === ')') {
      stack.pop();
    } else if (char !== ' ' && char !== '\n') {
      let numStr = char;
      while (i + 1 < input.length && /\d/.test(input[i + 1])) {
        numStr += input[++i];
      }
      const newNode = new TreeNode(parseInt(numStr));
      if (stack.length > 0) {
        stack[stack.length - 1].children.push(newNode);
      } else {
        root = newNode;
      }
      current = newNode.value;
    }
  }

  return root;
}


// And this function to print the parsed tree 


function printTree(node, depth = 0) {
  const indent = '  '.repeat(depth);
  console.log(`${indent}value: ${node.value}`);
  if (node.children.length > 0) {
    console.log(`${indent}children: [`);
    node.children.forEach((child) => printTree(child, depth + 1));
    console.log(`${indent}]`);
  }
}

const parsed = parseInput(input);
console.log(printTree(parsed));

value: 1
children: [
  value: 2
  value: 2
  children: [
    value: 4
    value: 5
    value: 6
    value: 6
    children: [
      value: 7
    ]
    value: 108
    value: 108
    children: [
      value: 9
    ]
  ]
  value: 3
]

Nodes, that have children, get double printed. I.E the output should be like this -

value: 1
children: [
  value: 2
  children: [
    value: 4
    value: 5
    value: 6
    children: [
      value: 7
    ]
    value: 108
    children: [
      value: 9
    ]
  ]
  value: 3
]

PLS, give me at least a hint at what wrong with my code, I have a bit more then an hour to send it!!!

Tinkering the code, commenting out the code, asking AI, searching web

Answer 1

You could simply make a JSON with an array data structure by replacing round brackets with square bracktes and spaces with comma. Then build a new data structure.

class Node {
    constructor(value) {
        this.value = value;
        this.children = [];
    }
}

const
    fn = array => {
        const result = [];
        let node;
        for (const value of array) {
            if (Array.isArray(value)) node.children.push(...fn(value));
            else result.push(node = new Node(value));
        }
        return result;
    },
    input = "(1 (2 (4 5 6 (7) 108 (9)) 3))",
    data = JSON.parse(input.replace(/\(/g, '[').replace(/\)/g, ']').replace(/ /g, ',')),
    result = fn(data);
    
console.log(result);

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