Functional backtracking: eight queens

Functional backtracking: eight queens.markdown

Functional backtracking: eight queens

A Pen by Sergiu Buciuc on CodePen.

License.

script.js

let allQueensSet = state => state.length == 8

let not = fn => (x) => !fn(x)
let lastNotUniq = R.converge(R.contains, [R.last, R.init])

let findIndexed = R.addIndex(R.findIndex)
let areDiagonal = (x1, y1, x2, y2) => Math.abs(x1-x2) === Math.abs(y1-y2)
let diagonalConflict = (x, arr) => -1 !== findIndexed(areDiagonal.bind(null, x, arr.length), arr)
let lastHasDiagonalConflict = R.converge(diagonalConflict,[R.last, R.init])

let queensConflict = R.anyPass([lastNotUniq, lastHasDiagonalConflict])
let queenOnNextLineEachColumn = state => R.map(col => ([...state, col]), R.times(R.identity, 8))

let eightQueensProblemSolver = backtracking({
  isSolution: allQueensSet,
  notValid: queensConflict,
  nextStates: queenOnNextLineEachColumn,
  initialState: [],
})

for (let solution of eightQueensProblemSolver()) {
  console.log(solution)
}

scripts

<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-polyfill/6.6.1/polyfill.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.19.1/ramda.js"></script>
<script src="http://codepen.io/sergiub/pen/wGKXpj"></script>