# [LeetCode] 349. Intersection of Two Arrays 两个数组相交

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.

class Solution {
public:
vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
unordered_set<int> st(nums1.begin(), nums1.end()), res;
for (auto a : nums2) {
if (st.count(a)) res.insert(a);
}
return vector<int>(res.begin(), res.end());
}
};

class Solution {
public:
vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
vector<int> res;
int i = 0, j = 0;
sort(nums1.begin(), nums1.end());
sort(nums2.begin(), nums2.end());
while (i < nums1.size() && j < nums2.size()) {
if (nums1[i] < nums2[j]) ++i;
else if (nums1[i] > nums2[j]) ++j;
else {
if (res.empty() || res.back() != nums1[i]) {
res.push_back(nums1[i]);
}
++i; ++j;
}
}
return res;
}
};

class Solution {
public:
vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
unordered_set<int> res;
sort(nums2.begin(), nums2.end());
for (auto a : nums1) {
if (binarySearch(nums2, a)) {
res.insert(a);
}
}
return vector<int>(res.begin(), res.end());
}
bool binarySearch(vector<int> &nums, int target) {
int left = 0, right = nums.size();
while (left < right) {
int mid = left + (right - left) / 2;
if (nums[mid] == target) return true;
else if (nums[mid] < target) left = mid + 1;
else right = mid;
}
return false;
}
};

class Solution {
public:
vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
set<int> s1(nums1.begin(), nums1.end()), s2(nums2.begin(), nums2.end()), res;
set_intersection(s1.begin(), s1.end(), s2.begin(), s2.end(), inserter(res, res.begin()));
return vector<int>(res.begin(), res.end());
}
};

Github 同步地址：

https://github.com/grandyang/leetcode/issues/349

Intersection of Two Arrays II

Find Common Characters

https://leetcode.com/problems/intersection-of-two-arrays/

https://leetcode.com/problems/intersection-of-two-arrays/discuss/81969/Three-Java-Solutions

https://leetcode.com/problems/intersection-of-two-arrays/discuss/82001/8ms-concise-C%2B%2B-using-unordered_set

posted @ 2016-05-18 23:33  Grandyang  阅读(25735)  评论(5编辑  收藏  举报