(lleetcode)Single Number

Given an array of integers, every element appears twice except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

1)使用map

class Solution {
public:
int singleNumber(vector<int>& nums) {
unordered_map<int,int> ret;
int i =;
while(i < nums.size())
{
ret[nums[i]]++;
i++;
}
for(unordered_map<int,int>::iterator it = ret.begin();it != ret.end(); ++it)
{
if(it->second == )
{
return it->first;break;
}
}
}
};
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