資訊專欄INFORMATION COLUMN
摘要：先想到的是，其實也可以，只是需要在遍歷的時候，添加到數(shù)組中的數(shù)要掉，略微麻煩了一點。在里跑的時候，也要快一點。另一種類似做法的就快的多了。如果是找出所有包括重復的截距呢
Problem
Given two arrays, write a function to compute their intersection.
NoticeEach element in the result must be unique.
The result can be in any order.
Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2].
ChallengeCan you implement it in three different algorithms?
Note先想到的是HashSet()，其實HashMap也可以，只是需要在遍歷nums2的時候，添加到res數(shù)組中的數(shù)要remove掉，略微麻煩了一點。在LC里跑的時候，HashSet也要快一點。
另一種類似HashMap做法的BitSet()就快的多了。
public class Solution {
public int[] intersection(int[] nums1, int[] nums2) {
Set set1 = new HashSet();
Set set2 = new HashSet();
List ans = new ArrayList();
for (int i = 0; i < nums1.length; i++) set1.add(nums1[i]);
for (int i = 0; i < nums2.length; i++) {
if (set1.contains(nums2[i])) set2.add(nums2[i]);
}
int[] res = new int[set2.size()];
int index = 0;
for (Integer i: set2) res[index++] = i;
return res;
}
}
BitSet
public class Solution {
public int[] intersection(int[] nums1, int[] nums2) {
int[] res = new int[nums1.length];
if (nums1.length == 0 || nums2.length == 0) return new int[0];
int index = 0;
BitSet set = new BitSet();
for (int i = 0; i < nums1.length; i++) {
set.set(nums1[i]);
}
for (int i = 0; i < nums2.length; i++) {
if (set.get(nums2[i]) == true) {
res[index++] = nums2[i];
set.set(nums2[i], false);
}
}
return Arrays.copyOfRange(res, 0, index);
}
}
Follow Up
如果是找出所有包括重復的截距呢？-- Intersection of Two Arrays II
public class Solution {
public int[] intersect(int[] nums1, int[] nums2) {
int k = 0, l1 = nums1.length, l2 = nums2.length;
int[] result = new int[l1];
Arrays.sort(nums1);
Arrays.sort(nums2);
int i = 0, j = 0;
while (i < l1 && j < l2)
if (nums1[i] < nums2[j]) i++;
else if (nums1[i] == nums2[j++]) result[k++] = nums1[i++];
return Arrays.copyOf(result, k);
}
}
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