Hard backtracking · recursion · grids

Quiet queens

Eight queens on one chessboard, and not one of them allowed to see another.

Write countQueens(n): count the ways to place n queens on an n by n board so that no two share a row, a column or a diagonal. n is at least 1.

Keep a board of 0s and 1s (1 is a queen) and call show(board) each time you complete a full placement. The stage draws every solution you find.

Example: countQueens(4) returns 2.

Tests you can see

countQueens(4)2
countQueens(1)1
countQueens(5)10

More tests are hidden. The server runs them all before a time counts.

Call show() while your code works and the run plays back here.

javascriptcountQueens()

function countQueens(n) {
  const board = Array.from({ length: n }, () => new Array(n).fill(0));
  let count = 0;
  // place one queen per row, back up when a row has no safe square
  return count;
}

function countQueens(n) {
  const board = Array.from({ length: n }, () => new Array(n).fill(0));
  let count = 0;
  // place one queen per row, back up when a row has no safe square
  return count;
}

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