LeetCode349、350. 两个数组的交集

 分析：使用集合

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

 

 

方法1：使用Map

class Solution {
    public int[] intersect(int[] nums1, int[] nums2) {
        Map<Integer,Integer> map = new HashMap<>();
        for (int num : nums1) {
            map.put(num,map.getOrDefault(num,0) + 1);
        }
        List<Integer> list = new ArrayList<>();
        for (int num : nums2) {
            if (map.containsKey(num)) {
                list.add(num);
                map.put(num,map.get(num) - 1);
                if (map.get(num) == 0) {
                    map.remove(num);
                }
            }
        }
        int[] res = new int[list.size()];
        int index = 0;
        for (int n : list) {
            res[index ++] = n;
        }
        return res;
    }
}

 

方法2：排序