The following is incorrect for finding a missing number in a sequence. func foo( _ nums: [Int] ) -> Int { var sum = 0 var _ = nums.map {sum += $0}

The following is incorrect for finding a missing number in a sequence. func foo( _ nums: [Int] ) -> Int { var sum = 0 var _ = nums.map {sum += $0} return (nums.count * ((nums.count+1) / 2)) - sum } The last line should be return ((nums.count+1) * ((nums.count+2) / 2)) - sum The count of nums will give the incorrect answer since it's already missing a value.