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]

解題思路：

用unordered_map掃描一遍。

?

class Solution {
public:
vector<int> findDuplicates(vector<int>& nums) {

unordered_map<int,int> store;
vector<int> duplicate;
for(int i=0;i<nums.size();i++){

if(store.count(nums[i]) == 1) {
duplicate.push_back(nums[i]);
}
else{
store[nums[i]]++;
}

}

return duplicate;
}
};

轉載于:https://www.cnblogs.com/liangyc/p/8783807.html

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