LeetCode Q005 Longest Palindromic Substring

Q005 Longest Palindromic Substring



 defines f(i...j): string[i...j] is palindrome or not
 if i == j, we are checking ''
 or j - i == 1  'a', j - i == 2, 'aa', just need to make sure stirng[i] ==  string[j]
 j - i > 2, we have to check if stirng[i] ==  string[j] and f[i+1...j-1]

 f(i...j) = string[i] ==  string[j]  && (j - i < 3 || f(i+1...j-1))
 So we need a 2D array to store results of sub problems

https://github.com/Sylvia-YiyinShen/Algorithm/blob/master/DynamicProgramming/Q005LongestPalindrome.playground/Contents.swift