题解 | #查找重复元素#

方法1

function duplicates(arr) {
    let demo = {};
    let res = [];
    arr.forEach(e => {
        if (demo[e]) {
            demo[e]++;
        } else {
            demo[e] = 1;
        }
    })
    for (const key in demo) {
        if (demo[key] > 1) {
            res.push(parseFloat(key));
        }
    }
    return res;
}

方法2

function duplicates(arr) {
    let res = [];
    res = arr.filter((e, i) => {
        return arr.indexOf(e) == i && arr.lastIndexOf(e) != i
    })
    return res;
}