string_palindromes_test.cc

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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  SOFTWARE.
*/
 
 
# include <gtest/gtest.h>
 
# include <String_Palindromes.H>
 
using namespace Aleph;
 
TEST(StringPalindromes, ManacherOddPalindrome)
{
  const auto r = manacher("abacaba");
  EXPECT_EQ(r.longest_palindrome, "abacaba");
  EXPECT_EQ(r.longest_begin, 0u);
  EXPECT_EQ(r.longest_length, 7u);
  ASSERT_EQ(r.odd_radius.size(), 7u);
  EXPECT_EQ(r.odd_radius[3], 4u);
}
 
TEST(StringPalindromes, ManacherEvenPalindrome)
{
  const auto r = manacher("abba");
  EXPECT_EQ(r.longest_palindrome, "abba");
  EXPECT_EQ(r.longest_begin, 0u);
  EXPECT_EQ(r.longest_length, 4u);
  ASSERT_EQ(r.even_radius.size(), 4u);
  EXPECT_GE(r.even_radius[2], 2u);
}
 
TEST(StringPalindromes, ManacherRepeatedCharacter)
{
  const auto r = manacher("aaaa");
  EXPECT_EQ(r.longest_palindrome, "aaaa");
  EXPECT_EQ(longest_palindromic_substring("aaaa"), "aaaa");
}
 
TEST(StringPalindromes, ManacherEmpty)
{
  const auto r = manacher("");
  EXPECT_TRUE(r.odd_radius.is_empty());
  EXPECT_TRUE(r.even_radius.is_empty());
  EXPECT_EQ(r.longest_length, 0u);
  EXPECT_EQ(r.longest_palindrome, "");
}
 
TEST(StringPalindromes, ManacherSingleChar)
{
  const auto r = manacher("x");
  EXPECT_EQ(r.longest_palindrome, "x");
  EXPECT_EQ(r.longest_length, 1u);
  EXPECT_EQ(r.longest_begin, 0u);
}
 
TEST(StringPalindromes, ManacherNoPalindromeAbove1)
{
  // "abcdef" — no palindrome longer than 1 character
  const auto r = manacher("abcdef");
  EXPECT_EQ(r.longest_length, 1u);
}
 
TEST(StringPalindromes, ManacherLongPalindrome)
{
  // Build a long palindrome: "abcba" repeated structure
  std::string half = "abcdefghijklmnopqrstuvwxyz";
  std::string palindrome = half;
  std::string rev_half(half.rbegin(), half.rend());
  palindrome += rev_half;
 
  const auto r = manacher(palindrome);
  EXPECT_EQ(r.longest_length, palindrome.size());
  EXPECT_EQ(r.longest_palindrome, palindrome);
}
 
TEST(StringPalindromes, ManacherWholeStringPalindrome)
{
  const auto r = manacher("xxxracecarxxx");
  EXPECT_EQ(r.longest_palindrome, "xxxracecarxxx");
  EXPECT_EQ(r.longest_length, 13u);
}
 
TEST(StringPalindromes, ManacherStressRepeatedPattern)
{
  // 1000 chars all same letter — entire string is a palindrome
  const std::string text(1000, 'z');
  const auto r = manacher(text);
  EXPECT_EQ(r.longest_length, 1000u);
  EXPECT_EQ(r.longest_palindrome, text);
}
 
// --- 3.4 Manacher: verify radius arrays directly ---
 
TEST(StringPalindromes, OddRadiusArrayAbacaba)
{
  // "abacaba"
  //  Char:       a  b  a  c  a  b  a
  //  odd_radius: 1  2  1  4  1  2  1
  //  index 1: "aba" centered at 'b' -> radius 2
  //  index 3: "abacaba" centered at 'c' -> radius 4
  //  index 5: "aba" centered at 'b' -> radius 2
  const auto r = manacher("abacaba");
  ASSERT_EQ(r.odd_radius.size(), 7u);
  EXPECT_EQ(r.odd_radius[0], 1u);
  EXPECT_EQ(r.odd_radius[1], 2u);
  EXPECT_EQ(r.odd_radius[2], 1u);
  EXPECT_EQ(r.odd_radius[3], 4u);
  EXPECT_EQ(r.odd_radius[4], 1u);
  EXPECT_EQ(r.odd_radius[5], 2u);
  EXPECT_EQ(r.odd_radius[6], 1u);
}
 
TEST(StringPalindromes, EvenRadiusArrayAbba)
{
  // "abba"
  //  even_radius[i] = max k such that text[i-k..i-1] == rev(text[i..i+k-1])
  //  i=0: 0, i=1: 0, i=2: 2 ("abba"), i=3: 0
  const auto r = manacher("abba");
  ASSERT_EQ(r.even_radius.size(), 4u);
  EXPECT_EQ(r.even_radius[0], 0u);
  EXPECT_EQ(r.even_radius[1], 0u);
  EXPECT_EQ(r.even_radius[2], 2u);
  EXPECT_EQ(r.even_radius[3], 0u);
}
 
TEST(StringPalindromes, OddRadiusArrayAllSame)
{
  // "aaaa"
  //  i=0: radius 1, i=1: radius 2, i=2: radius 2, i=3: radius 1
  const auto r = manacher("aaaa");
  ASSERT_EQ(r.odd_radius.size(), 4u);
  EXPECT_EQ(r.odd_radius[0], 1u);
  EXPECT_EQ(r.odd_radius[1], 2u);
  EXPECT_EQ(r.odd_radius[2], 2u);
  EXPECT_EQ(r.odd_radius[3], 1u);
}
 
TEST(StringPalindromes, EvenRadiusArrayAllSame)
{
  // "aaaa" even radii
  //  i=0: 0, i=1: 1, i=2: 2, i=3: 1
  const auto r = manacher("aaaa");
  ASSERT_EQ(r.even_radius.size(), 4u);
  EXPECT_EQ(r.even_radius[0], 0u);
  EXPECT_EQ(r.even_radius[1], 1u);
  EXPECT_EQ(r.even_radius[2], 2u);
  EXPECT_EQ(r.even_radius[3], 1u);
}
 
TEST(StringPalindromes, RadiusBruteForceVerification)
{
  // Verify Manacher's radius arrays against brute-force for a test string
  const std::string text = "abcbaXcbcYaabaa";
  const size_t n = text.size();
  const auto r = manacher(text);
 
  ASSERT_EQ(r.odd_radius.size(), n);
  ASSERT_EQ(r.even_radius.size(), n);
 
  // Brute-force verify odd radii
  for (size_t i = 0; i < n; ++i)
    {
      size_t k = 1;
      while (i >= k and i + k < n and text[i - k] == text[i + k])
        ++k;
      EXPECT_EQ(r.odd_radius[i], k) << "odd_radius mismatch at i=" << i;
    }
 
  // Brute-force verify even radii
  for (size_t i = 0; i < n; ++i)
    {
      size_t k = 0;
      while (i >= k + 1 and i + k < n and text[i - k - 1] == text[i + k])
        ++k;
      EXPECT_EQ(r.even_radius[i], k) << "even_radius mismatch at i=" << i;
    }
}
 
TEST(StringPalindromes, RadiusSingleCharString)
{
  const auto r = manacher("x");
  ASSERT_EQ(r.odd_radius.size(), 1u);
  ASSERT_EQ(r.even_radius.size(), 1u);
  EXPECT_EQ(r.odd_radius[0], 1u);
  EXPECT_EQ(r.even_radius[0], 0u);
}
 
TEST(StringPalindromes, RadiusTwoChars)
{
  {
    const auto r = manacher("ab");
    ASSERT_EQ(r.odd_radius.size(), 2u);
    EXPECT_EQ(r.odd_radius[0], 1u);
    EXPECT_EQ(r.odd_radius[1], 1u);
    EXPECT_EQ(r.even_radius[0], 0u);
    EXPECT_EQ(r.even_radius[1], 0u);
  }
  {
    const auto r = manacher("aa");
    ASSERT_EQ(r.odd_radius.size(), 2u);
    EXPECT_EQ(r.odd_radius[0], 1u);
    EXPECT_EQ(r.odd_radius[1], 1u);
    EXPECT_EQ(r.even_radius[0], 0u);
    EXPECT_EQ(r.even_radius[1], 1u);
  }
}
 
TEST(StringPalindromes, RadiusStressRandomString)
{
  // Build a 2000-character string and verify radii match brute force
  std::string text;
  text.reserve(2000);
  for (int i = 0; i < 2000; ++i)
    text.push_back('a' + (i * 7 + 3) % 4); // small alphabet
 
  const size_t n = text.size();
  const auto r = manacher(text);
 
  ASSERT_EQ(r.odd_radius.size(), n);
  ASSERT_EQ(r.even_radius.size(), n);
 
  for (size_t i = 0; i < n; ++i)
    {
      size_t k = 1;
      while (i >= k and i + k < n and text[i - k] == text[i + k])
        ++k;
      EXPECT_EQ(r.odd_radius[i], k);
    }
 
  for (size_t i = 0; i < n; ++i)
    {
      size_t k = 0;
      while (i >= k + 1 and i + k < n and text[i - k - 1] == text[i + k])
        ++k;
      EXPECT_EQ(r.even_radius[i], k);
    }
}