Sudoku Validator

sudokuValidator.js

// Given the grid below, create a function that determines
// if the grid is a valid sudoku

const grid = [
  ['.', '.', '.', '1', '4', '.', '.', '2', '.'],
  ['.', '.', '6', '.', '.', '.', '.', '.', '.'],
  ['.', '.', '.', '.', '.', '.', '.', '.', '.'],
  ['.', '.', '1', '.', '.', '.', '.', '.', '.'],
  ['.', '6', '7', '.', '.', '.', '.', '.', '9'],
  ['.', '.', '.', '.', '.', '.', '8', '1', '.'],
  ['.', '3', '.', '.', '.', '.', '.', '.', '6'],
  ['.', '.', '.', '.', '.', '7', '.', '.', '.'],
  ['.', '.', '.', '5', '.', '.', '.', '7', '.']
]

// Rules for validation
// In a sudoku, each row, column and cell (designated 3x3 boxes)
// must have the numbers 1-9 and only once
//
// I am not solving the sudoku, so I'm making the assumption
// that currently we are concerned with uniqueness
// Thus, if we filter the dots, we can test that each number
// in each array is unique. If it is unique, thus far we have a
// valid sudoku

function validateSudoku (grid) {
  return validateRows(grid) && validateColumns(grid) && validateCells(grid)
}

function validateRows (grid) {
  return grid.map(row => validatePart(row)).reduce(reduceBools, true)
}

function validateColumns (grid) {
  const columns = grid.reduce((acc, row) => {
    // First pass, create 9 empty arrays
    if (acc.length === 0) {
      for (let i = 0; i < 9; i++) {
        acc.push([])
      }
    }

    // For each row, push each item into the array at that index
    row.forEach((r, index) => {
      acc[index].push(r)
    })

    return acc
  }, [])

  return columns.map(col => validatePart(col)).reduce(reduceBools, true)
}

function validateCells (grid) {
  const cells = grid.reduce((gridAcc, row, gridIndex) => {
    // First pass, create 9 empty arrays
    if (gridAcc.length === 0) {
      for (let i = 0; i < 9; i++) {
        gridAcc.push([])
      }
    }

    const rowWithGroups = row.reduce((acc, cur, rowIndex) => {
      if (rowIndex < 3) {
        acc[0].push(cur)
      } else if (rowIndex < 6) {
        acc[1].push(cur)
      } else {
        acc[2].push(cur)
      }

      return acc
    }, [[], [], []])

    if (gridIndex < 3) {
      rowWithGroups.forEach((group, groupIndex) => {
        gridAcc[groupIndex] = [ ...gridAcc[groupIndex], ...group ]
      })
    } else if (gridIndex < 6) {
      rowWithGroups.forEach((group, groupIndex) => {
        gridAcc[groupIndex + 3] = [ ...gridAcc[groupIndex + 3], ...group ]
      })
    } else {
      rowWithGroups.forEach((group, groupIndex) => {
        gridAcc[groupIndex + 6] = [ ...gridAcc[groupIndex + 6], ...group ]
      })
    }

    return gridAcc
  }, [])

  return cells.map(cell => validatePart(cell)).reduce(reduceBools, true)
}

function validatePart (array) {
  const noDots = array.filter(i => i !== '.')
  const uniqItems = noDots.reduce((acc, cur) => {
    const index = acc.findIndex(item => item === cur)

    if (index === -1) {
      acc.push(cur)
    }

    return acc
  }, [])

  return uniqItems.length === noDots.length
}

function reduceBools (state, bool) {
  if (!bool) {
    state = false
  }

  return state
}

console.log(validateSudoku(grid)) // true