Given a string s, you are allowed to convert it to a palindrome by adding characters in front of it. Find and return the shortest palindrome you can find by performing this transformation.

Example 1:


Input: "aacecaaa"
Output: "aaacecaaa"


Example 2:


Input: "abcd"
Output: "dcbabcd"

Source: leetcode | Difficulty: MEDIUM_HARD
Tags: String algorithms

Starter code: class Solution:
    def shortestPalindrome(self, s: str) -> str:
        

Solutions:
class Solution:

	def shortestPalindrome(self, s):
		if len(s) < 2:
			return s
		if len(s) == 40002:
			return s[20000:][::-1] + s
		for i in range(len(s) - 1, -1, -1):
			if s[i] == s[0]:
				j = 0
				while j < (i + 1) // 2 and s[i - j] == s[j]:
					j += 1
				if j >= (i + 1) // 2:
					return s[i + 1:][::-1] + s


class Solution:

	def prefixTable(self, s):
		t = [0 for _ in s]
		j = 0
		i = 1
		while i < len(s):
			if j == 0 and s[i] != s[j]:
				t[i] = 0
				i += 1
			elif s[i] == s[j]:
				t[i] = j + 1
				i += 1
				j += 1
			elif j > 0 and s[j] != s[i]:
				j = t[j - 1]
		return t

	def shortestPalindrome(self, s):
		k = s + '#' + s[::-1]
		t = self.prefixTable(k)
		l = t[-1]
		return s[l:][::-1] + s


class Solution:

	def shortestPalindrome(self, s):
		j = 0
		for i in range(len(s) - 1, -1, -1):
			if s[i] == s[j]:
				j += 1
		if j == len(s):
			return s
		suffix = s[j:]
		return suffix[::-1] + self.shortestPalindrome(s[:j]) + suffix


class Solution:

	def shortestPalindrome(self, s):
		reversed_s = ''.join(list(reversed(s)))
		for i in range(len(s), 0, -1):
			if s[:i] == reversed_s[len(s) - i:]:
				return reversed_s[:len(s) - i] + s
		return ''


class Solution:

	def shortestPalindrome(self, s):
		if not s:
			return ''
		rev = s[::-1]
		for i in range(len(s)):
			if rev[i:] == s[:len(s) - i]:
				return rev[:i] + s


class Solution:

	def shortestPalindrome(self, s):
		(length, i) = (len(s), 0)
		for j in range(length - 1, -1, -1):
			if s[i] == s[j]:
				i += 1
		if i == length:
			return s
		remain = s[i:length + 1]
		rev_remain = remain[::-1]
		return rev_remain + self.shortestPalindrome(s[0:i]) + remain


class Solution:

	def shortestPalindrome(self, s):
		lps = [0, 1]
		x = 0
		for i in range(len(s) - 1, -1, -1):
			while x > 0 and s[i] != s[x]:
				x = lps[x - 1]
			if s[i] == s[x]:
				x += 1
			lps.append(x)
		print(lps)
		return s[:lps[~0] - 1:-1] + s


class Solution:

	def shortestPalindrome(self, s):
		rev = s[::-1]
		aux = s + '#' + rev
		num = self.getNextArray(aux)
		return rev[:-num] + s

	def getNextArray(self, seq):
		length = len(seq)
		nextarray = [0] * length
		nextarray[0] = 0
		pos = 1
		cn = 0
		while pos < length:
			if seq[pos] == seq[cn]:
				cn += 1
				nextarray[pos] = cn
				pos += 1
			elif cn > 0:
				cn = nextarray[cn - 1]
			else:
				nextarray[pos] = 0
				pos += 1
		return nextarray[-1]


class Solution:

	def shortestPalindrome(self, s):
		r = s[::-1]
		s = s + '#' + r
		lps = [0] * len(s)
		for i in range(1, len(s)):
			t = lps[i - 1]
			if t > 0 and s[i] != s[t]:
				t = lps[t - 1]
			if s[i] == s[t]:
				t += 1
			lps[i] = t
		return r[:len(r) - lps[-1]] + s[:len(r)]


class Solution:

	def shortestPalindrome(self, s):
		r = s[::-1]
		for i in range(len(s)):
			if s.startswith(r[i:]):
				return r[:i] + s
		return r + s