LeetCode——Find All Duplicates in an Array

Question

Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.

Find all the elements that appear twice in this array.

Could you do it without extra space and in O(n) runtime?

Example:

Input:
[4,3,2,7,8,2,3,1]
Output:
[2,3]

Solution

哈希，顺便复习一下STL中set容器用法。

Code

class Solution {
public:
    vector<int> findDuplicates(vector<int>& nums) {
        set<int> table;
        vector<int> res;
        for (int i : nums) {
            if (table.find(i) == table.end())
                table.insert(i);
            else
                res.push_back(i);
        }
        return res;
    }
};