#Strings

Solve a modified version of the standard Valid Parentheses problem.

Given a string, count how many palindromic substrings it contains.

Write a Java program to generate and print all permutations of a given string.

Given two strings, S and T, find the minimum window in S which will contain all the characters of T. If there is no such window, return the empty string. Example: Input: S = 'ADOBECODEBANC', T = 'ABC'. Output: 'BANC'.

Given a string 's' and an integer 'k', return the length of the longest substring of 's' such that the frequency of each character in this substring is greater than or equal to 'k'.