find common elements in two arrays

Solution 1:

if not sorted, sorted arrays first , use two pointers to point to each array, 谁小移谁

Solution 2 : ( for one array size <<<< another array size)

use hash table to store the smaller table's <element, count> pair. Loop through the bigger array, for each element if contains in the hash table and count > = 1, add to result.

Solution 3: (for one array size <<<< another array size)

binary search , for each element (as target) from smaller array, run binary search against the bigger array.

( if duplicate element included in the result, actually this solution is not easy implemented )