[leetcode]349. Intersection of Two Arrays数组交集

Given two arrays, write a function to compute their intersection.

Example 1:

Input: nums1 = [1,2,2,1], nums2 = [2,2]
Output: [2]

Example 2:

Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4]
Output: [9,4]

 

题意：

如题

 

Solution1：  HashSet

1.  Scan nums1,  put items in nums1 to set1

2. Scan nums2, check each item is contained in set1 

     

   

 

注意： HashSet.contains() -> O(1) 

 

code

class Solution {
  public int[] intersection(int[] nums1, int[] nums2) {
        HashSet <Integer> set1 = new HashSet<>(); 
        HashSet <Integer> resSet = new HashSet<>(); 
        
        for (int i = 0; i < nums1.length; i ++) {
            set1.add(nums1[i]);
        }
        for (int i = 0; i < nums2.length; i ++) {
            if (set1.contains(nums2[i])) {  
                resSet.add(nums2[i]);
            }
        } 
        //  resSet -> int[]res
        int [] res = new int[resSet.size()];
        int index = 0;
        for (int num : resSet) {
            res[index++] = num;
        }
        return res;
    }
}