题解 | #查找重复元素#

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function duplicates(arr) {
    const target = [];
    const map = new Map();
    arr.forEach(v => {
        if(map.has(v) && !target.includes(v)) {
            target.push(v);
        } else {
            map.set(v, v);
        }
    });
    return target;
}