LeetCode 349 Intersection of Two Arrays

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

Example:

Given nums1 = 

[1, 2, 2, 1]

, nums2 = 

[2,
2]

, return 

[2]

.

Note:

Each element in the result must be unique.

The result can be in any order.
方法一：使用set

public int[] intersection(int[] nums1, int[] nums2) {
Set<Integer> set = new HashSet<Integer>();
for (int i = 0; i < nums1.length; i++)
set.add(nums1[i]);
int[] result = new int[nums2.length];
int k = 0;
for (int i = 0; i < nums2.length; i++)
if (set.contains(nums2[i])) {
result[k++] = nums2[i];
set.remove(nums2[i]); //一定要删除
}
return Arrays.copyOfRange(result, 0, k);
}

方法二：先排序，比方法一效率略高。因为方法一里，for循环调用HashSet.contains(
)，而HashSet.contains( )效率并不是O(1)。

public int[] intersection2(int[] nums1, int[] nums2) {
Arrays.sort(nums1);
Arrays.sort(nums2);
int[] result = new int[nums2.length];
int i = 0, j = 0, k = 0;
while (i < nums1.length && j < nums2.length) {
if (nums1[i] < nums2[j]) {
i++;
} else if (nums1[i] > nums2[j]) {
j++;
} else {
result[k++] = nums1[i++];
while (i < nums1.length && nums1[i] == nums2[j]) i++;
j++;
}
}
return Arrays.copyOfRange(result, 0, k);
}