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LeetCode Intersection of Two Arrays 349

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.

自己的解法

使用 set 进行去重

public static int[] intersection2(int[] nums1, int[] nums2) {
	Set<Integer> nums1Set = new HashSet<>();
	Set<Integer> set = new HashSet<>();
	for (int integer : nums1) {
		nums1Set.add(integer);
	}
	for (int integer : nums2) {
		if (nums1Set.contains(integer)) {
			set.add(integer);
		}
	}
	int[] result = new int[set.size()];
	int i = 0;
	for (int integer : set) {
		result[i] = integer;
		i++;
	}
	return result;
}

别人的思路

LeetCode – Intersection of Two Arrays (Java)

Binary Search

public int[] intersection(int[] nums1, int[] nums2) {
    Arrays.sort(nums1);
    Arrays.sort(nums2);
    ArrayList<Integer> list = new ArrayList<Integer>();
    for(int i=0; i<nums1.length; i++){
        if(i==0 || (i>0 && nums1[i]!=nums1[i-1])){
            if(Arrays.binarySearch(nums2, nums1[i])>-1){
                list.add(nums1[i]);
            }
        }
    }
    int[] result = new int[list.size()];
    int k=0;
    for(int i: list){
        result[k++] = i;
    }
    return result;
}

Time = O(nlog(n)).
Space = O(n).