[Anagrams] Reduce memory cost

By changing `map<string, string>` to `map<string, int>` to reduce memory cost.
no twisted mathematical hack
amend the explanation of the second solution
Merge branch 'patch-1' of https://github.com/jakwings/leetcode into jakwings-patch
Merge branch 'patch-4' of https://github.com/jakwings/leetcode into jakwings-patch
add some comments
Merge branch 'patch-3' of https://github.com/jakwings/leetcode into jakwings-patch
add some comments
Merge branch 'jakwings-patch'