1. Longest substring palindrome from a string
2.Generate parentheses
Input -- n=1 output -- ()
Input -- n=2 output -- ()() (())
3.input -- (A, D), (B, E), (F, G), (D, P) (P, O) (L, A)
Apple
Output -- true
Only one character from each set to from the word
4. Find the missing number from an consecutive numbers of array
input -- {1,2,3,5,}
output -- 4
