Given a string, find all dominant palindromes. For a given string, a dominant palindrome is a palindrome ocurring in the string that is longer than 1 letter and is not a substring of another palindrome in the string.
For example, for string
abcbabb, there are three such
palindromes as follows.
Input. The input consists of one or more strings, each on a line of its own. The input is terminated by EOF. The following is a sample input file.
Output. For each input string, the output consists of an output case. An output case consists of the input string, followed by the dominant palindromes in any order, followed by a blank line. The following is the output file that corresponds to the sample input file.
Given a string of length
n, the proposed solution takes
We illustrate our solution on the following string
We determine the dominant palindromes from left to right in two steps. We determine the longest palindrome greater than one character for each position and then discard palindromes that are subsumed.
s, the longest palindromes are the following. For
position 3 the longest palindrome is
bcb, for position 4 is
for position 5 is
bab, and for position 6 is
s, there is only one subsumed palindrome. That
palindrome is the one for position 3 and the dominant palindrome is
the one for position 4.
To determine longest palindromes we apply the following rules.
When there is a palindrome for a position, the longest palindrome is
either a continuation of a previous longest palindrome or a new
palindrome. For example, for position 3 the longest palindrome
is new because the characters in positions 1 and 3 are the
same. Another example, for position 4 the longest palindrome
is a continuation of the palindrome for position 3 because the
characters in positions 0 and 4 are the same.
When there is no palindrome, neither condition is true. For example, for position 2 there is no palindrome because there is no palindrome for position 1 and the characters in positions 0 and 2 are different.
When a position corresponds to a new palindrome, the reason is that either the character two positions before is the same or the character in the previous position is the same. For example, position 3 is a new palindrome because the character two positions before is the same. Another example, position 6 is a new palindrome because the previous character is the same.
When the apply the rules for longest palindromes to each position, we annotate the position with the start position of the longest palindrome if any, like so.
Given the list of start positions, we determine the dominant palindromes by moving from left to right on the list, dropping any previous start position that is greater than the current start position because those are subsumed, like so.
Given that a previous palindrome can only be subsumed when we determine a longest palindrome, we drop subsumed palindromes as we determine palindromes in the following way.
When we continue a palindrome, we drop the start position for the previous position because we just subsumed the longest palindrome for the previous position. For example, for position 4 we continue the palindrome for position 3, and so we drop the start position for position 3.
When we find a new longest palindrome of length 2, there is nothing to drop, because any palindrome for the previous position starts before the previous position. For example, for position 6, the palindrome for position 5 starts in position 3.
When we find a new longest palindrome of length 3 at position
drop the previous start position when that start position is
i - 2.
For example, consider the start and dominant positions of string
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