linear-list/array/intersection-of-two-arrays

Intersection of Two Arrays

描述

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

Example 1:

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

Example 2:

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

Note:

• Each element in the result must be unique.
• The result can be in any order.

分析

思路一，可以把两个数组排序，然后用两个指针，同时遍历两个数组，时间复杂度 O(nlogn+mlogm)，空间复杂度 O(logm + logn) 到 O(m+n) 之间，取决于排序算法。

思路二，建两个 HashSet, 然后集合求交集，时间复杂度 O(m + n))，空间复杂度 O(m + n)。

代码

// Intersection of Two Arrays
// Two HashSet
// Time Complexity: O(m+n), Space Complexity: O(m+n)
class Solution {
  public int[] intersection(int[] nums1, int[] nums2) {
    Set<Integer> set1 = new HashSet<Integer>();
    for (int n : nums1) set1.add(n);
    Set<Integer> set2 = new HashSet<Integer>();
    for (int n : nums2) set2.add(n);

    set1.retainAll(set2);

    int [] result = new int[set1.size()];
    int i = 0;
    for (int s : set1) result[i++] = s;
    return result;
  }
}

// TODO

相关题目

• Intersection of Two Arrays II