Algorithm to evenly distribute items into 3 columns

Question

I'm looking for an algorithm that will evenly distribute 1 to many items into three columns. No column can have more than one more item than any other column. I typed up an example of what I'm looking for below. Adding up Col1,Col2, and Col3 should equal ItemCount.

Edit: Also, the items are alpha-numeric and must be ordered within the column. The last item in the column has to be less than the first item in the next column.

Items         Col1,Col2,Col3
A             A
AB            A,B
ABC           A,B,C
ABCD          AB,C,D
ABCDE         AB,CD,E
ABCDEF        AB,CD,EF
ABCDEFG       ABC,DE,FG
ABCDEFGH      ABC,DEF,GH
ABCDEFGHI     ABC,DEF,GHI
ABCDEFHGIJ    ABCD,EFG,HIJ
ABCDEFHGIJK   ABCD,EFGH,IJK

Answer 1

Here you go, in Python:

NumCols = 3
DATA = "ABCDEFGHIJK"

for ItemCount in range(1, 12):
    subdata = DATA[:ItemCount]

    Col1Count = (ItemCount + NumCols - 1) / NumCols
    Col2Count = (ItemCount + NumCols - 2) / NumCols
    Col3Count = (ItemCount + NumCols - 3) / NumCols

    Col1 = subdata[:Col1Count]
    Col2 = subdata[Col1Count:Col1Count+Col2Count]
    Col3 = subdata[Col1Count+Col2Count:]

    print "%2d   %5s  %5s  %5s" % (ItemCount, Col1, Col2, Col3)

# Prints:
#  1       A              
#  2       A      B       
#  3       A      B      C
#  4      AB      C      D
#  5      AB     CD      E
#  6      AB     CD     EF
#  7     ABC     DE     FG
#  8     ABC    DEF     GH
#  9     ABC    DEF    GHI
# 10    ABCD    EFG    HIJ
# 11    ABCD   EFGH    IJK