counting duplicates in a sorted sequence using command line tools

how about;

$ echo "100 100 100 99 99 26 25 24 24" \
    | tr " " "\n" \
    | sort \
    | uniq -c \
    | sort -k2nr \
    | awk '{printf("%s\t%s\n",$2,$1)}END{print}'

The result is :

100 3
99  2
26  1
25  1
24  2