Setting a value to duplicate datas using countif

[Araxxor]

Currently facing a problem with duplicate datas.

Invoice no.	Unique No.	Item Desc
1000123456	1	Pliers
1000123456	0	Nail
1000123456	0	Hammers
1222444444	1	Paper
1444222222	1	Nail
1223456789	1	Nail
1000123456	0	Planks
1112223334	1	Saw
1112223334	0	Hammer

<tbody>
</tbody>

So i would like to set those invoice numbers in the Unique No. column, those with duplicates a value of 1, (first entry of 1000123456 to 1, the rest a value of 0). Other invoice numbers with no duplicates (1222444444, 1444222222, etc to 1)

I tried using excel's sort and filter function but since my data has gaps in between, the rows without any data was set to 0 as well.

My goal is to find the number of Invoices issued without double counting the duplicates.

Any help is appreciated. Thanks in advance

 

[Momentman]

Maybe like this (feeling like formula is unnecessarily lengthy )

Excel 2010
	A	B	C	D
1	Invoice no.	Unique No.	Item Desc
2	1000123456	1	Pliers
3	1000123456	0	Nail
4	1000123456	0	Hammers
5	1222444444	1	Paper
6	1444222222	1	Nail
7	1223456789	1	Nail
8	1000123456	0	Planks
9		0
10	1112223334	1	Saw
11	1112223334	0	Hammer
Sheet2

Cell Formulas
Range	Formula
B2	=IF(COUNTIF($A$2:$A$11,A2)=1,1,IF(AND(COUNTIF($A$2:$A$11,A2)>1,COUNTIF($A$2:A2,A2)=1),1,0))

 

[Weazel]

maybe something like...

Excel 2012

	A	B	C
1	Invoice no.	Unique No.	Item Desc
2	1000123456	1	Pliers
3	1000123456	0	Nail
4	1000123456	0	Hammers
5	1222444444	1	Paper
6	1444222222	1	Nail
7	1223456789	1	Nail
8	1000123456	0	Planks
9
10	1112223334	1	Saw
11	1112223334	0	Hammer

<colgroup><col style="width: 25pxpx"><col><col><col></colgroup><thead>
</thead><tbody>
</tbody>

Sheet2​

Worksheet Formulas Cell Formula B2 =IF(A2="","",N(COUNTIF($A$2:A2,A2)=1)) <thead> </thead><tbody> </tbody>

<tbody>
</tbody>