136. Single Number
Given a non-empty array of integers num, each element appears twice except one. Find the one and only.
You need to implement a solution with linear complexity at runtime and use only constant extra space.
Example 1:
Input: nums = [2,2,1]
Output: 1
Example 2:
Input: nums = [4,1,2,1,2]
Output: 4
Example 3:
Input: nums = [1]
Output: 1
Limitations:
1 <= count.length <= 3 * 104
-3 * 104 <= nums[i] <= 3 * 104
Each element in the array appears twice except for one element which appears only once.
Solution
class Solution {
public:
int singleNumber(vector& nums) {
unordered_map a;
for(auto x: nums)
a[x]++;
for(auto z:a)
if(z.second==1)
return z.first;
return -1;
}
};
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