Delete repeated rows keeping one closer to another file using awk - shell

Question

I have two files
$cat file1.txt
0105 20 20 95 50
0106 20 20 95 50
0110 20 20 88 60
0110 20 20 88 65
0115 20 20 82 70
0115 20 20 82 70
0115 20 20 82 75
If you see the file1.txt, there are repeated values in column-1, which are 0110 and 0115.
So I would like to keep one row only based on the column-5 values, which are closer to corresponding values in a reference file (file2.txt). Here closer means the equal or the nearest value in file2.txt. I don't want to change any value in file1.txt, but just to select one row.
$cat file2.txt
0105 20 20 95 50
0106 20 20 95 50
0107 20 20 95 52
0110 20 20 88 65 34
0112 20 20 82 80 23
0113 20 20 82 85 32
0114 20 20 82 70 23
0115 20 20 82 72
0118 20 20 87 79
0120 20 20 83 79
So if we compare the two files, we must keep 0110 20 20 88 65, as the column-5 entry (i.e. 65) in file1.txt is closer that in reference file (i.e. 65 in file2.txt) and delete the other repeated rows. Similarly we must keep 0115 20 20 82 70 because 70 is closer to 72 and delete other two rows starting with 0115
Desire output:
0105 20 20 95 50
0106 20 20 95 50
0110 20 20 88 65
0115 20 20 82 70
I am trying with the following script, but not getting my desire result.
awk 'FNR==NR { a[$5]; next } $5 in a ' file1.txt file2.txt > test.txt
awk '{a[NR]=$1""$2} a[NR]!=a[NR-1]{print}' test.txt
My fortran program algorithm is:
# check each entries in column-1 in file1.txt with next rows if they are same or not
i.e. for i=1,i++ do # Here i is ith row
for j=1,j++ do
if a[i,j] != a[i+1,j]; then print the whole row as it is,
else
# find the row b[i,j] in file2.txt starting with a[i,j]
# and compare the 5th column i.e. b[i,j+5] with all a[i,j+5] starting with a[i,j] in file1.txt
# and take the differences to find closest one
e.g. if we have 3 rows starting with same entry, then
we select the a[i,j] in which diff(b[i,j+5],a[i,j+5]) is minumum i=1,2,3

Answer 1

awk 'BEGIN {
while ((getline line < "file2.txt")>0) {
split(line, f);
file2[f[1]] = line;
}
}
{
if (!($1 in result)) result[$1] = $0;
split(result[$1], a);
split(file2[$1], f);
if (abs(f[5]-$5) < abs(f[5]-a[5])) result[$1] = $0;
}
END {
for (i in result) print result[i];
}
function abs(n) {
return (n < 0 ? -n : n);
}' file1.txt | sort