Cracking the Cryptic webapp helper

idea.md

Cracking the Cryptic sudoku webapp helper

This just detects if you've made a clear error as you're solving something (only looks at the basic sudoku rules, nothing fancy):

To install, just open your developer console (⌘⇧I or Cmd Shift I, then select console) and paste in the source code below:

sudoku-helper.js

const grid = $('.sudoku-grid')
const cells = grid.querySelectorAll('.sudoku-cell__inner')

function check() {
  for (let i = 0; i < 9; i++) {
    for (let j = 0; j < 9; j++) {
      const a = i * 9 + j
      cells[a].style.boxShadow = ''
      const val_a = cells[a].querySelector('.sudoku-cell__value')
      cells[a].__value = val_a ? val_a.innerText : null
    }
  }

  for (let i = 0; i < 9; i++) {
    for (let j = 0; j < 9; j++) {
      const a = i * 9 + j
      const val_a = cells[a].__value
      if (!val_a) continue

      for (let k = i; k < 9; k++) {
        for (let l = 0; l < 9; l++) {
          if (k === i && l < j) continue

          const same_row = i === k
          const same_col = j === l
          if (same_row && same_col) continue

          const same_region =
            Math.floor(i / 3) === Math.floor(k / 3) &&
            Math.floor(j / 3) === Math.floor(l / 3)
          if (!(same_row || same_col || same_region)) continue

          const b = k * 9 + l
          const same_value = val_a === cells[b].__value
          if (same_value) {
            console.log(
              `Cell ${i + 1},${j + 1} and ${k + 1},${l + 1} are both ${val_a}`
            )
            cells[a].style.boxShadow = 'inset 0 0 4px 4px red'
            cells[b].style.boxShadow = 'inset 0 0 4px 4px red'
          }
        }
      }
    }
  }
}

const observer = new MutationObserver(check)

cells.forEach(cell =>
  observer.observe(cell, {
    childList: true,
    subtree: true,
    characterData: true
  })
)