TheAlgorithms/JavaScript · error · TypeError

Grid must only contain 0s and 1s

Error message

Grid must only contain 0s and 1s

What it means

Thrown by validateGrid() when any cell is not strictly 0 or 1. The maze uses 1 for open path and 0 for wall, and isSafe() compares grid[y][x] === 1 with strict equality, so the string "1", booleans, null, or 2/3 would break path detection.

Source

Thrown at Backtracking/RatInAMaze.js:37

 * - must not contain values other than {@code 0} and {@code 1}
 *
 * @param grid The grid to check.
 * @throws TypeError When the given grid is invalid.
 */
function validateGrid(grid) {
  if (!Array.isArray(grid) || grid.length === 0)
    throw new TypeError('Grid must be a non-empty array')

  const allRowsHaveCorrectLength = grid.every(
    (row) => row.length === grid.length
  )
  if (!allRowsHaveCorrectLength) throw new TypeError('Grid must be a square')

  const allCellsHaveValidValues = grid.every((row) => {
    return row.every((cell) => cell === 0 || cell === 1)
  })
  if (!allCellsHaveValidValues)
    throw new TypeError('Grid must only contain 0s and 1s')
}

function isSafe(grid, x, y) {
  const n = grid.length
  return x >= 0 && x < n && y >= 0 && y < n && grid[y][x] === 1
}

/**
 * Attempts to calculate the remaining path to the target.
 *
 * @param grid The full grid.
 * @param x The current X coordinate.
 * @param y The current Y coordinate.
 * @param solution The current solution matrix.
 * @param path The path we took to get from the source cell to the current location.
 * @returns {string|boolean} Either the path to the target cell or false.
 */
function getPathPart(grid, x, y, solution, path) {

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Normalize all cells to numbers 0 or 1 before solving.
2. If parsing from text, map with Number() or +cell and reject anything outside {0,1}.
3. Keep a separate visited/seen structure instead of encoding extra states into the grid.

Example fix

// before
const grid = rawText.split('\n').map(r => r.split(''))
// after
const grid = rawText
  .trim().split('\n')
  .map(r => r.trim().split('').map(Number))

function isBinaryGrid(g) {
  return Array.isArray(g) && g.length > 0 &&
    g.every(r => Array.isArray(r) && r.every(c => c === 0 || c === 1));
}
// grid = grid.map(r => r.map(Number)); before solving

/** @param {unknown} g @returns {g is (0|1)[][]} */
function isBinaryGrid(g) {
  return Array.isArray(g) && g.length > 0 &&
    g.every(r => Array.isArray(r) && r.every(c => c === 0 || c === 1));
}

try { solve(grid); }
catch (e) {
  if (e instanceof TypeError && /0s and 1s/.test(e.message)) {
    grid = grid.map(r => r.map(c => Number(c)));
  } else throw e;
}

When it happens

Trigger: Cells containing "1" (string from JSON/text), 2, true/false, null, undefined, NaN, or any numeric value other than 0 or 1.

Common situations: Reading the maze from a text file or CSV where values arrive as strings, or storing tristate flags (e.g. 2 = visited) inside the source grid.

Related errors

• Grid must be a non-empty array
• Grid must be a square
• Input data must be type of Array

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/c406bae0a6cfb507. Report an issue: GitHub.