一道有关转换树形数据结构的JS面试题

Question

请写出一个名为transTree的函数，实现如下功能

    var arr1 = [
        { level: 1 },
        { level: 2 },
        { level: 3 },
        { level: 1 }
    ];
    var arr2 = [
        { h: 2 },
        { h: 4 },
        { h: 2 },
        { h: 3 }
    ]
    var newArr1 = transTree(arr1, 'level');
    var newArr2 = transTree(arr2, 'h');

    console.log(newArr1);
    /*newArr1
    [
        {
            level: 1,
            sub: [
                {
                    level: 2,
                    sub: [
                        { level: 3 }
                    ]
                }
            ],
        },
        {
            level: 1
        }
    ]
     */

    console.log(newArr2);
    /*newArr2
    [
        {
            h: 2,
            sub: [
                { h: 4 }
            ]
        },
        {
            h: 2,
            sub: [
                { h: 3 }
            ]
        }
    ]
     */

Answer 1

没人回答？好吧，撸一串,供参考

function transTree(list, attr) {
    var result = [];
    list.reduce(function (res, cur, index, arr) {
        var prev = res[res.length - 1];
        if (prev && cur[attr] > prev[attr]) {
            if (!prev.sub) prev.sub = [];
            prev.sub.push(cur);
            if (index === arr.length - 1) prev.sub = transTree(prev.sub, attr);
        } else {
            res.push(cur);
            if (prev && prev.sub) prev.sub = transTree(prev.sub, attr);
        }
        return res;
    }, result);
    return result;
}