n-queens.js

/**
 * Get all solutions of `n queens` problem
 * https://zh.wikipedia.org/wiki/%E5%85%AB%E7%9A%87%E5%90%8E%E9%97%AE%E9%A2%98
 * @param n
 * @returns {*}
 * @constructor
 */
const Nqueens = n => {
  if (typeof n !== 'number') {
    console.warn('Expect `n` to be a number got ' + typeof n + '.');
    return;
  }

  if (n < 4) {
    console.warn('No solution.');
    return;
  }

  const row = n;
  const col = n;
  const result = [];
  const results = [];

  let i = 0;
  let start = 0;

  while (i >= 0 && i < row) {
    let success = false;
    for (let j = start; j < col; j++) {
      if (success || result.some(r => {
        const [
          ri,
          rj
        ] = r;

        return ri === i || rj === j || Math.abs(ri - i) === Math.abs(rj - j);
      })) {
        continue;
      }

      result.push([i, j]);
      success = true;
    }

    if (success) {
      i++;
      start = 0;
    }

    if (result.length === col) {
      results.push(result.concat());
    }

    if (result.length === col || !success) {
      const last = result.pop();
      if (last) {
        start = last[1] + 1;
        i--;
      } else {
        i--;
        start = 0;
      }
    }
  }

  return results;
}