function queen(n, decisions=[], decisionSet=new Set()) {

  if (decisions.length === n) {

    /***过滤重复内容*********/

    decisions.sort((a,b) => a-b);

    const hash = decisions.join('-');

    if (decisionSet.has(hash)) return [];

    decisionSet.add(hash);

    /**********************/

    return [decisions];

  }

  let r = [];

  for(let i = 0;i < n*n; i++) {

    if(decisions.indexOf(i) === -1) {

      // 保证遍历的内容不存在攻击

      if (decisions.every(item => compatible(item, i, n))) {

        r = r.concat(queen(n, decisions.concat(i), decisionSet))

      }

    }

  }

  return r;

}

//判断decisions是否符合要求,数组内两两比较

function is_goal(n, decisions) {

  for(let i = 0; i < n; i++) {

    for(let j = i+1; j < n; j++) {

      if(i===j) continue;

      const p = decisions[i];

      const q = decisions[j];

      if(!compatible(p,q,n)) {

        return false

      }

    }

  }

  return true;

}

function compatible(p,q,n) {// 判断位置p,q是否存在互相攻击

  const [x1, y1] = [~~(p/n), p % n];

  const [x2, y2] = [~~(q/n), q % n];

  return x1!==x2 && y1!==y2 && Math.abs(x1-x2) !== Math.abs(y1-y2)

}