# 349.Intersection-of-Two-Arrays

## ้ข็ฎๅฐๅ

https://leetcode.com/problems/intersection-of-two-arrays/

## ้ข็ฎๆ่ฟฐ

``````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]

Note:
Each element in the result must be unique.
The result can be in any order.``````

## ไปฃ็ 

### Approach #1 Two Sets

``````class Solution {
public int[] intersection(int[] nums1, int[] nums2) {
HashSet<Integer> set1 = new HashSet<Integer>();
HashSet<Integer> set2 = new HashSet<Integer>();

if (set1.size() < set2.size()) {
return helper(set1, set2);
} else {
return helper(set2, set1);
}
}

private int[] helper(HashSet<Integer> set1, (HashSet<Integer> set2) {
int[] output = new int[set1.size()];
int idx = 0;
for (Integer s: set1) {
if (set2.contains(s)) {
output[idx++] = s;
}
}
return Arrays.copyOf(output, idx);
}
}``````

### Approach #2 Built-in Set Intersection

``````class Solution {
public int[] intersection(int[] nums1, int[] nums2) {
HashSet<Integer> set1 = new HashSet<Integer>();
for (Integer n : nums1) set1.add(n);
HashSet<Integer> set2 = new HashSet<Integer>();
for (Integer n : nums2) set2.add(n);

set1.retainAll(set2);

int [] output = new int[set1.size()];
int idx = 0;
for (int s : set1) output[idx++] = s;
return output;
}
}``````

### Approach #3 Two Pointer

``````public class Solution {
public int[] intersection(int[] nums1, int[] nums2) {
Set<Integer> set = new HashSet<>();
Arrays.sort(nums1);
Arrays.sort(nums2);
int i = 0;
int j = 0;
while (i < nums1.length && j < nums2.length) {
if (nums1[i] < nums2[j]) {
i++;
} else if (nums1[i] > nums2[j]) {
j++;
} else {
i++;
j++;
}
}
int[] result = new int[set.size()];
int k = 0;
for (Integer num : set) {
result[k++] = num;
}
return result;
}
}``````

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