function arrConcat (arrA, arrB) {
    const res = [],
        dir = {};
    let pointerA = 0,
        pointerB = 0;
    while (pointerA < arrA.length && pointerB < arrB.length) {
        let temp;
        //将较小的值推到栈中
        if (arrA[pointerA] > arrB[pointerB]) {
            temp = arrB[pointerB++];
        }
        else {
            temp = arrA[pointerA++];
        }
        
        //字典记录添加过的数据
        if (!dir.hasOwnProperty(temp)) {
            res.push(temp);
            dir[temp] = true;
        }
    }

    //没有遍历到尾部的数组
    const otherData = arrA.slice(pointerA).concat(arrB.slice(pointerB));
    res.push(...otherData);

    console.log(res);//[1,2,4,5,6]
}
arrConcat([1,2,4,5],[2,4,6])