Q:

Find cells with opposite duplicates

Trying to code something to find cells with same amount but opposite value.
A few additional rules: 

1, all cells are in a column;
2, match aims to find pairs of values for example, (1 and -1, 2.0003 and - 2.0003, 31.3245678 and
-31.3245678)--- if there are 3 of 1 and 4 of -1, only highlight 3 pairs of 1 and -1, leaving the extra -1 in the list without
highlighting;
3, once a pair is highlighted, the pair is no longer considered in following match. that means, match continues for
all remaining cells until all pairs in the column are found.

In the following picture, you can find a few pairs are highlighted, remaining cells are not matched, therefore remain in unfilled color.

A:

You can just use something like the following formula 
=COUNTIF(A:A,-A:A)

To show how many negative duplicates a value has

To get only the first matching negatives use the following formula:
=IF(COUNTIF(A:A,-A:A)>=COUNTIF(A$1:A1,A1),TRUE,FALSE)

or even shorter
=COUNTIF(A:A,-A:A)>=COUNTIF(A$1:A1,A1)

