⚡️ Speed up function is_palindrome by 44%

[codeflash-ai]

📄 44% (0.44x) speedup for is_palindrome in src/dsa/various.py

⏱️ Runtime : 699 microseconds → 486 microseconds (best of 956 runs)

📝 Explanation and details

The optimized code achieves a 43% speedup by eliminating the expensive string preprocessing step and using a two-pointer approach that processes characters in-place.

Key Optimization: Eliminated String Construction
The original code creates an entirely new cleaned string using "".join(c.lower() for c in text if c.isalnum()), which is the performance bottleneck (58.6% of total time). This involves:

• Iterating through every character once
• Creating intermediate strings for each character
• Memory allocation for the new string
• String concatenation overhead

The optimized version eliminates this preprocessing entirely by using two pointers that skip non-alphanumeric characters on-the-fly during comparison.

Two-Pointer In-Place Processing
Instead of creating a cleaned string, the optimized code:

• Uses left and right pointers starting from string ends
• Advances pointers past non-alphanumeric characters using while loops
• Compares characters directly with .lower() only when needed
• Short-circuits immediately on first mismatch

Performance Analysis by Test Case Type:

1. Massive speedup for early-exit cases: Non-palindromes see 200-8500% speedups (e.g., "python" 300% faster, large non-palindromes 7500+ % faster) because the two-pointer approach can return False after checking just the first differing pair, while the original must still process the entire string upfront.

2. Moderate speedup for true palindromes: True palindromes see 30-85% speedups because both approaches must check most/all characters, but the optimized version avoids the preprocessing overhead and string allocation costs.

3. Slight slowdown for non-alphanumeric heavy strings: Cases with many consecutive non-alphanumeric characters (like "!@#$%^&*()") can be 12-62% slower because the pointer advancement loops add overhead when there are few actual character comparisons to perform.

Memory Efficiency: The optimized approach uses O(1) additional space versus O(n) for creating the cleaned string, reducing memory pressure and cache misses.

The optimization is most effective for inputs with early mismatches or moderate amounts of non-alphanumeric characters, making it ideal for real-world palindrome checking where most inputs are not palindromes.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 72 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	✅ 2 Passed
📊 Tests Coverage	100.0%

🌀 Generated Regression Tests and Runtime

import string  # used for generating large test cases

# imports
import pytest  # used for our unit tests
from src.dsa.various import is_palindrome

# unit tests

# ------------------
# Basic Test Cases
# ------------------

def test_simple_palindrome():
    # Even length palindrome
    codeflash_output = is_palindrome("abba") # 916ns -> 541ns (69.3% faster)
    # Odd length palindrome
    codeflash_output = is_palindrome("racecar") # 583ns -> 333ns (75.1% faster)
    # Single character
    codeflash_output = is_palindrome("a") # 292ns -> 83ns (252% faster)
    # Two different characters
    codeflash_output = is_palindrome("ab") # 375ns -> 125ns (200% faster)
    # Simple non-palindrome
    codeflash_output = is_palindrome("python") # 500ns -> 125ns (300% faster)

def test_case_insensitivity():
    # Palindrome with mixed case
    codeflash_output = is_palindrome("AbBa") # 916ns -> 500ns (83.2% faster)
    codeflash_output = is_palindrome("RaceCar") # 583ns -> 333ns (75.1% faster)

def test_ignores_non_alphanumeric():
    # Palindrome with spaces and punctuation
    codeflash_output = is_palindrome("A man, a plan, a canal: Panama") # 2.12μs -> 1.58μs (34.2% faster)
    # Palindrome with symbols
    codeflash_output = is_palindrome("No 'x' in Nixon") # 958ns -> 583ns (64.3% faster)
    # Non-palindrome with symbols
    codeflash_output = is_palindrome("Hello, world!") # 750ns -> 208ns (261% faster)

# ------------------
# Edge Test Cases
# ------------------

def test_empty_string():
    # An empty string is trivially a palindrome
    codeflash_output = is_palindrome("") # 541ns -> 125ns (333% faster)

def test_only_non_alphanumeric():
    # Only spaces
    codeflash_output = is_palindrome("   ") # 625ns -> 458ns (36.5% faster)
    # Only punctuation
    codeflash_output = is_palindrome("!!!") # 292ns -> 250ns (16.8% faster)
    # Mixed non-alphanumeric
    codeflash_output = is_palindrome(" . , ! ") # 292ns -> 291ns (0.344% faster)

def test_numbers_and_alphanumeric():
    # Numeric palindrome
    codeflash_output = is_palindrome("12321") # 1.00μs -> 541ns (84.8% faster)
    # Numeric non-palindrome
    codeflash_output = is_palindrome("12345") # 541ns -> 208ns (160% faster)
    # Alphanumeric palindrome
    codeflash_output = is_palindrome("1a2b2a1") # 584ns -> 375ns (55.7% faster)
    # Alphanumeric non-palindrome
    codeflash_output = is_palindrome("1a2b3c") # 500ns -> 166ns (201% faster)

def test_unicode_characters():
    # Palindrome with accented characters (should treat as different)
    codeflash_output = is_palindrome("réer") # 1.04μs -> 583ns (78.6% faster)
    # Palindrome with unicode, ignoring non-alphanumeric
    codeflash_output = is_palindrome("あいいあ") # 791ns -> 458ns (72.7% faster)
    # Mixed unicode and ascii
    codeflash_output = is_palindrome("aあa") # 500ns -> 166ns (201% faster)

def test_long_palindromic_and_non_palindromic():
    # Palindrome with repeated characters
    codeflash_output = is_palindrome("aaaaaa") # 1.04μs -> 625ns (66.6% faster)
    # Non-palindrome with repeated characters
    codeflash_output = is_palindrome("aaaaaab") # 542ns -> 166ns (227% faster)

# ------------------
# Large Scale Test Cases
# ------------------

def test_large_even_length_palindrome():
    # Construct a large palindrome (1000 characters)
    half = "abc123" * 83 + "abc1"  # 500 chars
    palindrome = half + half[::-1]
    codeflash_output = is_palindrome(palindrome) # 58.5μs -> 44.5μs (31.3% faster)

def test_large_odd_length_palindrome():
    # Construct a large odd-length palindrome (999 characters)
    half = "xyz987" * 83 + "xyz9"  # 499 chars
    palindrome = half + "Q" + half[::-1]
    codeflash_output = is_palindrome(palindrome) # 57.7μs -> 44.1μs (30.8% faster)

def test_large_non_palindrome():
    # Large string that is not a palindrome (999 chars)
    half = "abcdef" * 83 + "abcde"  # 499 chars
    non_palindrome = half + "Z" + half
    codeflash_output = is_palindrome(non_palindrome) # 32.4μs -> 416ns (7693% faster)

def test_large_with_non_alphanumeric():
    # Large palindrome with spaces and punctuation interleaved
    base = ("A1b2C3d4E5f6G7h8I9j0" * 25)[:500]  # 500 chars
    palindrome = base + base[::-1]
    # Insert spaces and punctuation every 10 chars
    decorated = ""
    for i, c in enumerate(palindrome):
        decorated += c
        if (i+1) % 10 == 0:
            decorated += " ,! "
    codeflash_output = is_palindrome(decorated) # 57.7μs -> 54.9μs (5.16% faster)

def test_performance_on_large_input():
    # Stress test: 1000-character non-palindrome, should be fast
    s = "a" * 999 + "b"
    codeflash_output = is_palindrome(s) # 31.9μs -> 416ns (7572% faster)

# ------------------
# Negative and Mutation-Resistant Cases
# ------------------

def test_only_first_and_last_characters_palindrome():
    # Not a palindrome if only first and last characters match
    codeflash_output = is_palindrome("abca") # 958ns -> 500ns (91.6% faster)

def test_palindrome_with_embedded_non_alphanumerics():
    # Palindrome with non-alphanumerics in the middle
    codeflash_output = is_palindrome("a@b#b@a") # 1.00μs -> 625ns (60.0% faster)

def test_non_palindrome_with_similar_halves():
    # Not a palindrome if halves are mirror but not full string
    codeflash_output = is_palindrome("abcddcbaX") # 1.08μs -> 375ns (189% faster)

def test_empty_after_cleaning():
    # String with only non-alphanumerics should be palindrome
    codeflash_output = is_palindrome("!!!...") # 666ns -> 541ns (23.1% faster)

def test_palindrome_with_mixed_case_and_numbers():
    # Palindrome with mixed case and numbers
    codeflash_output = is_palindrome("A1b2B1a") # 1.08μs -> 666ns (62.6% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

import string  # used for generating large test cases

# imports
import pytest  # used for our unit tests
from src.dsa.various import is_palindrome

# unit tests

# 1. Basic Test Cases

def test_simple_palindrome():
    # Simple palindrome, all lowercase
    codeflash_output = is_palindrome("madam") # 958ns -> 500ns (91.6% faster)

def test_simple_non_palindrome():
    # Simple non-palindrome
    codeflash_output = is_palindrome("hello") # 917ns -> 334ns (175% faster)

def test_palindrome_with_mixed_case():
    # Palindrome with mixed case
    codeflash_output = is_palindrome("RaceCar") # 1.08μs -> 625ns (73.3% faster)

def test_palindrome_with_spaces():
    # Palindrome with spaces
    codeflash_output = is_palindrome("nurses run") # 1.29μs -> 750ns (72.1% faster)

def test_non_palindrome_with_spaces():
    # Non-palindrome with spaces
    codeflash_output = is_palindrome("hello world") # 1.25μs -> 333ns (275% faster)

def test_palindrome_with_punctuation():
    # Palindrome with punctuation and spaces
    codeflash_output = is_palindrome("A man, a plan, a canal: Panama!") # 2.04μs -> 1.58μs (28.9% faster)

def test_non_palindrome_with_punctuation():
    # Non-palindrome with punctuation
    codeflash_output = is_palindrome("This is not a palindrome!") # 1.67μs -> 416ns (300% faster)

def test_numeric_palindrome():
    # Palindrome with numbers
    codeflash_output = is_palindrome("12321") # 1.00μs -> 542ns (84.5% faster)

def test_numeric_non_palindrome():
    # Non-palindrome with numbers
    codeflash_output = is_palindrome("12345") # 958ns -> 375ns (155% faster)

def test_alphanumeric_palindrome():
    # Palindrome with letters and numbers
    codeflash_output = is_palindrome("1a2b2a1") # 1.12μs -> 666ns (68.9% faster)

def test_alphanumeric_non_palindrome():
    # Non-palindrome with letters and numbers
    codeflash_output = is_palindrome("1a2b3c") # 1.00μs -> 375ns (167% faster)

# 2. Edge Test Cases

def test_empty_string():
    # Empty string should be considered a palindrome
    codeflash_output = is_palindrome("") # 541ns -> 166ns (226% faster)

def test_single_character():
    # Single character string is a palindrome
    codeflash_output = is_palindrome("a") # 625ns -> 166ns (277% faster)

def test_single_non_alphanumeric_character():
    # Single non-alphanumeric character is a palindrome (since cleaned is empty)
    codeflash_output = is_palindrome("!") # 625ns -> 166ns (277% faster)

def test_only_spaces():
    # String with only spaces is a palindrome (since cleaned is empty)
    codeflash_output = is_palindrome("     ") # 666ns -> 500ns (33.2% faster)

def test_only_punctuation():
    # String with only punctuation is a palindrome (since cleaned is empty)
    codeflash_output = is_palindrome("!!!...,,,") # 667ns -> 583ns (14.4% faster)

def test_two_characters_palindrome():
    # Two identical characters
    codeflash_output = is_palindrome("aa") # 833ns -> 416ns (100% faster)

def test_two_characters_non_palindrome():
    # Two different characters
    codeflash_output = is_palindrome("ab") # 833ns -> 333ns (150% faster)

def test_unicode_palindrome():
    # Palindrome with unicode characters (accented letters)
    codeflash_output = is_palindrome("été") # 916ns -> 500ns (83.2% faster)

def test_unicode_non_palindrome():
    # Non-palindrome with unicode characters
    codeflash_output = is_palindrome("étè") # 916ns -> 417ns (120% faster)

def test_mixed_unicode_and_ascii():
    # Palindrome with mixed unicode and ascii
    codeflash_output = is_palindrome("Añña") # 1.00μs -> 584ns (71.2% faster)

def test_long_string_with_only_non_alphanumeric():
    # Long string with only non-alphanumeric characters
    codeflash_output = is_palindrome("!@#$%^&*()_+-=,./;'[]\\<>?:\"{}|") # 916ns -> 1.04μs (12.0% slower)

def test_palindrome_with_newlines_and_tabs():
    # Palindrome with whitespace characters
    codeflash_output = is_palindrome("a\nb\tb\na") # 1.04μs -> 583ns (78.6% faster)

def test_non_palindrome_with_newlines_and_tabs():
    # Non-palindrome with whitespace characters
    codeflash_output = is_palindrome("a\nb\tc\na") # 1.04μs -> 583ns (78.6% faster)

def test_palindrome_with_leading_and_trailing_spaces():
    # Palindrome with leading and trailing spaces
    codeflash_output = is_palindrome("  abba  ") # 1.04μs -> 667ns (56.1% faster)

def test_palindrome_with_leading_and_trailing_punctuation():
    # Palindrome with leading/trailing punctuation
    codeflash_output = is_palindrome("!!madam!!") # 1.04μs -> 667ns (56.2% faster)

def test_case_insensitivity():
    # Palindrome with alternating cases
    codeflash_output = is_palindrome("AbBa") # 917ns -> 541ns (69.5% faster)

def test_non_palindrome_case_insensitivity():
    # Non-palindrome with alternating cases
    codeflash_output = is_palindrome("AbBc") # 875ns -> 375ns (133% faster)

def test_palindrome_with_numbers_and_letters_and_spaces():
    # Palindrome with numbers, letters, and spaces
    codeflash_output = is_palindrome("1 a 2 2 a 1") # 1.21μs -> 792ns (52.5% faster)

# 3. Large Scale Test Cases

def test_large_even_length_palindrome():
    # Large even-length palindrome
    half = ''.join(['a' for _ in range(500)])
    s = half + half[::-1]
    codeflash_output = is_palindrome(s) # 53.6μs -> 39.4μs (36.0% faster)

def test_large_odd_length_palindrome():
    # Large odd-length palindrome
    half = ''.join(['b' for _ in range(499)])
    s = half + 'x' + half[::-1]
    codeflash_output = is_palindrome(s) # 51.4μs -> 38.9μs (32.2% faster)

def test_large_non_palindrome():
    # Large non-palindrome (one character different)
    half = ''.join(['c' for _ in range(500)])
    s = half + 'd' + half[::-1]
    codeflash_output = is_palindrome(s) # 51.6μs -> 39.3μs (31.3% faster)

def test_large_palindrome_with_mixed_case_and_punctuation():
    # Large palindrome with mixed case and punctuation
    base = ''.join(['A' if i % 2 == 0 else 'b' for i in range(400)])
    s = base + "!!!" + base[::-1]
    codeflash_output = is_palindrome(s) # 41.6μs -> 31.5μs (31.8% faster)

def test_large_palindrome_with_numbers_and_letters():
    # Large palindrome with numbers and letters
    base = ''.join(['1a2b3c4d' for _ in range(50)])
    s = base + base[::-1]
    codeflash_output = is_palindrome(s) # 42.4μs -> 33.3μs (27.3% faster)

def test_large_string_only_non_alphanumeric():
    # Large string with only non-alphanumeric characters
    s = ''.join(['!' for _ in range(999)])
    codeflash_output = is_palindrome(s) # 8.29μs -> 21.7μs (61.7% slower)

def test_large_string_almost_palindrome():
    # Large string, almost palindrome (one character in the middle is off)
    base = ''.join(['x' for _ in range(499)])
    s = base + 'y' + base[::-1]
    codeflash_output = is_palindrome(s) # 51.5μs -> 39.1μs (31.8% faster)

def test_large_string_with_spaces_and_punctuation():
    # Large palindrome with spaces and punctuation
    base = ''.join(['a b, ' for _ in range(100)])
    s = base + base[::-1]
    codeflash_output = is_palindrome(s) # 26.6μs -> 32.0μs (16.7% slower)

def test_large_string_with_unicode():
    # Large palindrome with unicode characters
    base = ''.join(['é' for _ in range(400)])
    s = base + base[::-1]
    codeflash_output = is_palindrome(s) # 49.0μs -> 38.3μs (27.9% faster)

def test_large_string_with_varied_characters():
    # Large string with varied characters, not a palindrome
    s = ''.join([string.ascii_letters[i % 52] for i in range(999)])
    codeflash_output = is_palindrome(s) # 32.4μs -> 375ns (8533% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

from src.dsa.various import is_palindrome

def test_is_palindrome():
    is_palindrome('\u07fb˯¶Ļﵐ')

def test_is_palindrome_2():
    is_palindrome('\x00\x1f˭Ṉṉ')

To edit these changes git checkout codeflash/optimize-is_palindrome-mdpcje5v and push.