Sum of Unique Elements
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ArrayCountingHash Table
Write a function that takes an array of integers and returns the sum of the elements that appear only once in the array. For example, given the array [4, 3, 2, 4, 1, 2, 3], the function should return 1 because only the element 1 appears exactly once.
Example 1
Input
[ 4, 3, 2, 4, 1, 2, 3 ]
Output
1
Explanation. Only the number `1` appears exactly once in the array.
Example 2
Input
[ 7, 8, 9, 7, 9 ]
Output
8
Explanation. Only the number `8` appears exactly once in the array.
Example 3
Input
[ 1, 1, 1 ]
Output
0
Explanation. No number appears only once; hence, the sum is `0`.
Example 4
Input
[ 10 ]
Output
10
Explanation. The single number `10` appears exactly once, so the sum is `10`.
Follow-up: How would your solution change if the input array could contain both positive and negative integers?
Constraints:
The input array will contain at least one element and all elements will be integers.
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