// 回溯算法的练习，一行代码

var permute = nums => Array(1).fill().reduce(_ => Array(1).fill().reduce(__ => (__.backtrack([]), _._res), { backtrack: (_._backtrack = (path) => (path.length === nums.length && _._res.push(path), nums.filter(n => !path.includes(n)).forEach(n => _._backtrack(path.concat(n)))), _._backtrack) }), { _res: Array(0), _backtrack: void 0 });

permute([1,3,5])