Array notes

1. get the length:

    a. int array[len];    int len = array.length();

    b. vector<int> array;    int len = array.size();

2. print vector array    

for (int i = 0; i < len; i++) {
    print(nums[i]);
}

3. pay attention to the special cases

    for example: when the input is empty one!!!    -> answer

                         when the input is pretty large!!!    -> time