I have a site called abcd.com. in this site i have 2 minimal subsites in it (A and B).
search page exists in parent site that is abcd.com only.
when i click any link inside A or B site then my URL is abcd.com/A or abcd.com/B.
after navigating to A site when i search , search results should display within A or B only.
if my URL in browser abcd.com/A or abcd.com/B site and if am searching then serach results should be display from abcd.com/A or abcd.com/B only not inlcude all.
If I understand the issue correctly, you're looking for a way to limit the results you're returning from a search to only include content from within a section of the site (in your example, either A or B depending on the site the user is currently viewing). I think the way I'd approach that would be to filter using Ancestors() to limit results to those with an ancestor of the required section. Something like this:
if (currentSubsite == siteA)
ancestorContentRef = contentRefOfSiteA;
ancestorContentRef = contentRefOfSiteB;
var query = SearchClient.Instance.Search<MyContentType>()
.Filter(x => x.Ancestors().Match(ancestorContentRef.ToString()));