Question: A string is a palindrome if it is the same read left to right or right to left, e . g . ababa. The longest

A string is a palindrome if it is the same read left to right or right to left, e.g. ababa. The longest palindrome subsequence of a string x is its longest subsequence (of not necessarily consecutive symbols) that is a palindrome. We want an algorithm to determine in time O(|x|2) the length of the longest palindrome sub-sequence of a string x.(a) A cheap solution is, let y be the reverse of x, and apply the standard Longest Common Subsequence (LCS) algorithm to x and y. This approach is numerically correct, but flawed, since the character locations for a LCS in x and y does not have to reference the same sequence of physical characters. Suppose x is ZABZA, what are the LCS for x and its reverse? How many are they? Are they all palindrome? (b) A better way is to design a new DP algorithm. Let l(i, j) be the length of longest palindrome in x[i,..., j], please write the recurrence equations, including the initial conditions. Please analyze the time and space complexity.

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