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

Example 1:

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

Example 2:

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

Note:

• Each element in the result should appear as many times as it shows in both arrays.
• The result can be in any order.

給定兩個陣列，寫一個方法來計算它們的交集。

例如: 
給定 nums1 = [1, 2, 2, 1], nums2 = [2, 2], 返回 [2, 2].

注意：

• 輸出結果中每個元素出現的次數，應與元素在兩個陣列中出現的次數一致。
• 我們可以不考慮輸出結果的順序。

public class Solution {
	public int[] intersect(int[] nums1, int[] nums2) {
		TreeMap<Integer, Integer> map = new TreeMap<>();
		for (int num : nums1) {
			if (!map.containsKey(num))
				map.put(num, 1);
			else
				map.put(num, map.get(num) + 1);
		}
		ArrayList<Integer> res = new ArrayList<>();
		for (int num : nums2) {
			if (map.containsKey(num)) {
				res.add(num);
				map.put(num, map.get(num) - 1);
				if (map.get(num) == 0)
					map.remove(num);
			}
		}
		int[] ret = new int[res.size()];
		for (int i = 0; i < res.size(); i++)
			ret[i] = res.get(i);
		return ret;
	}
}
 

測試程式碼                           

public class Test {
	public static void main(String[] args) {
		int[] a = { 1, 2, 2, 1 };
		int[] b = { 2, 2 };
		Solution solution = new Solution();
		System.out.println(Arrays.toString(solution.intersect(a, b)));
	}
}
 

 執行結果