StringSliding WindowHash Map
Find the smallest substring of s that contains every character of t, including duplicates (if t has two a's the window needs two a's). If several windows have the minimum length, report the leftmost one.
Input
Line 1: the string s. Line 2: the string t.
Output
Print the smallest window, or None if no window contains all characters of t.
Constraints
1 <= length of s, t <= 10^5 Both strings contain English letters.
Example 1
Input
ADOBECODEBANC ABC
Output
BANC
BANC is the shortest window containing A, B and C.
Example 2
Input
a aa
Output
None
There is only one a, but t needs two.