力扣 LeetCode 349. 两个数组的交集（Day3：哈希表）

解题思路：

方法一：数组

class Solution {
    public int[] intersection(int[] nums1, int[] nums2) {
        int[] hash = new int[1001];

        Set<Integer> set = new HashSet<>();
        for (int i = 0; i < nums1.length; i++) hash[nums1[i]] = 1;
        for (int i = 0; i < nums2.length; i++)
            if (hash[nums2[i]] == 1) set.add(nums2[i]);

        int[] res = new int[set.size()];
        int cnt = 0;
        for (int s : set) res[cnt++] = s;
        
        return res;
    }
}

方法二：set

注意使用set.contains判断是否已有该值

class Solution {
    public int[] intersection(int[] nums1, int[] nums2) {
        Set<Integer> set = new HashSet<>();
        Set<Integer> res = new HashSet<>();

        for (int num1 : nums1) set.add(num1);
        for (int num2 : nums2)
            if (set.contains(num2)) res.add(num2);

        int[] ans = new int[res.size()];
        int cnt = 0;
        for (int x : res)
            ans[cnt++] = x;
            
        return ans;
    }
}