⚡️ Speed up function is_palindrome by 31%

[codeflash-ai]

📄 31% (0.31x) speedup for is_palindrome in src/dsa/various.py

⏱️ Runtime : 1.55 milliseconds → 1.19 milliseconds (best of 150 runs)

📝 Explanation and details

The optimized code achieves a 30% speedup by replacing string operations with list-based character comparisons and eliminating redundant string length calculations.

Key optimizations:

1. List vs String Operations: Changed from "".join() to [c.lower() for c in text if c.isalnum()]. While both have similar time complexity, the list approach avoids string concatenation overhead and provides direct indexed access.

2. Two-pointer Algorithm: Replaced the range-based loop with a two-pointer approach (left and right moving toward each other). This eliminates the repeated len(cleaned_text) - 1 - i calculation on every iteration - a significant improvement when checking longer strings.

3. Reduced Index Calculations: The original code calculated len(cleaned_text) - 1 - i for every character comparison. The optimized version pre-calculates positions and simply increments/decrements pointers.

Performance benefits by test case type:

• Short strings (1-10 chars): 30-100% faster due to reduced overhead
• Medium strings with punctuation: 25-35% faster from eliminating repeated length calculations
• Large palindromes (1000+ chars): 25-27% faster, where the elimination of redundant arithmetic operations has the most impact
• Non-alphanumeric heavy strings: Minimal improvement (3-6%) since most time is spent in the filtering step

The two-pointer approach is particularly effective for palindrome checking because it can exit early on the first mismatch, and when it does need to check the full string, it avoids the arithmetic overhead of computing reverse indices.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 114 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	✅ 2 Passed
🔮 Hypothesis Tests	✅ 100 Passed
📊 Tests Coverage	100.0%

🌀 Generated Regression Tests and Runtime

from __future__ import annotations

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

# unit tests

# 1. Basic Test Cases
def test_simple_palindromes():
    # Single character is always a palindrome
    codeflash_output = is_palindrome("a") # 1.33μs -> 750ns (77.9% faster)
    # Two identical characters
    codeflash_output = is_palindrome("aa") # 1.04μs -> 708ns (47.2% faster)
    # Simple palindrome
    codeflash_output = is_palindrome("madam") # 1.00μs -> 708ns (41.2% faster)
    # Simple non-palindrome
    codeflash_output = is_palindrome("hello") # 916ns -> 542ns (69.0% faster)
    # Palindrome with mixed case
    codeflash_output = is_palindrome("RaceCar") # 1.08μs -> 833ns (30.1% faster)
    # Palindrome with spaces and punctuation
    codeflash_output = is_palindrome("A man, a plan, a canal: Panama") # 2.96μs -> 2.25μs (31.5% faster)
    # Non-palindrome with spaces and punctuation
    codeflash_output = is_palindrome("This is not a palindrome!") # 2.29μs -> 1.75μs (31.0% faster)

def test_numeric_and_alphanumeric():
    # Numeric palindrome
    codeflash_output = is_palindrome("12321") # 2.00μs -> 1.42μs (41.1% faster)
    # Numeric non-palindrome
    codeflash_output = is_palindrome("12345") # 1.04μs -> 667ns (56.1% faster)
    # Alphanumeric palindrome
    codeflash_output = is_palindrome("1a2b2a1") # 1.33μs -> 1.00μs (33.3% faster)
    # Alphanumeric non-palindrome
    codeflash_output = is_palindrome("1a2b3c") # 958ns -> 625ns (53.3% faster)

# 2. Edge Test Cases
def test_empty_and_whitespace():
    # Empty string is trivially a palindrome
    codeflash_output = is_palindrome("") # 1.21μs -> 500ns (142% faster)
    # String with only spaces
    codeflash_output = is_palindrome("     ") # 875ns -> 542ns (61.4% faster)
    # String with only punctuation
    codeflash_output = is_palindrome("!!!") # 584ns -> 292ns (100% faster)
    # String with only mixed spaces and punctuation
    codeflash_output = is_palindrome("  ,,,  ") # 625ns -> 375ns (66.7% faster)

def test_unicode_and_special_characters():
    # Unicode palindrome (ignoring accents and non-alphanumeric)
    codeflash_output = is_palindrome("été") # 2.04μs -> 1.33μs (53.2% faster)
    # Unicode non-palindrome
    codeflash_output = is_palindrome("étéé") # 1.29μs -> 750ns (72.3% faster)
    # Emoji and symbols ignored (not alphanumeric)
    codeflash_output = is_palindrome("a😊a") # 917ns -> 584ns (57.0% faster)
    # Mixed unicode and alphanumeric
    codeflash_output = is_palindrome("A😊b😊A") # 917ns -> 583ns (57.3% faster)

def test_case_sensitivity_and_non_alphanum():
    # Case-insensitivity
    codeflash_output = is_palindrome("AbBa") # 1.96μs -> 1.25μs (56.6% faster)
    # Non-alphanumeric at ends
    codeflash_output = is_palindrome("!aba!") # 1.08μs -> 708ns (53.0% faster)
    # Non-alphanumeric in the middle
    codeflash_output = is_palindrome("a!b!a") # 792ns -> 541ns (46.4% faster)

def test_edge_length_cases():
    # Two different characters
    codeflash_output = is_palindrome("ab") # 1.71μs -> 958ns (78.3% faster)
    # Three characters, not a palindrome
    codeflash_output = is_palindrome("abc") # 875ns -> 458ns (91.0% faster)
    # Four characters, palindrome
    codeflash_output = is_palindrome("abba") # 917ns -> 708ns (29.5% faster)
    # Four characters, not a palindrome
    codeflash_output = is_palindrome("abca") # 833ns -> 500ns (66.6% faster)

def test_long_repetitive_palindrome():
    # Palindrome with repeated characters
    codeflash_output = is_palindrome("aaaaaa") # 2.04μs -> 1.46μs (40.1% faster)
    # Non-palindrome with one different character
    codeflash_output = is_palindrome("aaaaab") # 1.08μs -> 625ns (73.3% faster)

# 3. Large Scale Test Cases
def test_large_even_palindrome():
    # Large even-length palindrome
    s = "ab" * 500  # 'ababab...'
    palindrome = s + s[::-1]
    codeflash_output = is_palindrome(palindrome) # 169μs -> 132μs (27.7% faster)

def test_large_odd_palindrome():
    # Large odd-length palindrome
    s = "abc" * 333  # 999 characters
    palindrome = s + "x" + s[::-1]
    codeflash_output = is_palindrome(palindrome) # 161μs -> 126μs (27.0% faster)

def test_large_non_palindrome():
    # Large non-palindrome
    s = "abc" * 333
    non_palindrome = s + "y" + s[::-1]
    codeflash_output = is_palindrome(non_palindrome) # 159μs -> 126μs (26.6% faster)

def test_large_palindrome_with_noise():
    # Large palindrome with spaces and punctuation
    s = "xyZ" * 300
    palindrome = s + s[::-1]
    noisy = " " * 100 + palindrome + "!" * 100
    codeflash_output = is_palindrome(noisy) # 148μs -> 117μs (26.5% faster)

def test_large_string_only_non_alphanum():
    # Large string of only punctuation and spaces
    noisy = " " * 500 + "!" * 500
    codeflash_output = is_palindrome(noisy) # 16.5μs -> 15.6μs (5.33% faster)

# 4. Additional Robustness Cases
def test_mixed_alphanum_and_non_alphanum():
    # Palindrome with numbers and letters, and non-alphanum
    codeflash_output = is_palindrome("1a2!2a1") # 2.29μs -> 1.75μs (31.0% faster)
    # Non-palindrome with numbers and letters, and non-alphanum
    codeflash_output = is_palindrome("1a2!3a1") # 1.29μs -> 792ns (63.1% faster)

def test_false_positives():
    # Should not be fooled by mirrored non-alphanum
    codeflash_output = is_palindrome("a!b!c!b!a") # 2.04μs -> 1.58μs (29.0% faster)
    codeflash_output = is_palindrome("a!b!c!d!a") # 1.17μs -> 791ns (47.5% faster)

def test_palindrome_with_newlines_and_tabs():
    # Palindrome with newlines and tabs
    codeflash_output = is_palindrome("\nA\tb\tA\n") # 1.96μs -> 1.33μs (46.8% faster)
    # Non-palindrome with newlines and tabs
    codeflash_output = is_palindrome("\nA\tb\tC\n") # 1.04μs -> 583ns (78.7% faster)

# 5. Determinism and Consistency
def test_consistency_across_calls():
    # Call multiple times to check determinism
    for _ in range(10):
        codeflash_output = is_palindrome("Deified") # 10.9μs -> 7.38μs (48.0% faster)
        codeflash_output = is_palindrome("Python")
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.
#------------------------------------------------
from __future__ import annotations

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

# unit tests

# -------------------------
# BASIC TEST CASES
# -------------------------

def test_simple_palindromes():
    # Basic palindromic words
    codeflash_output = is_palindrome("madam") # 2.12μs -> 1.42μs (50.0% faster)
    codeflash_output = is_palindrome("deified") # 1.21μs -> 750ns (61.1% faster)
    codeflash_output = is_palindrome("civic") # 917ns -> 583ns (57.3% faster)
    codeflash_output = is_palindrome("level") # 833ns -> 541ns (54.0% faster)
    codeflash_output = is_palindrome("radar") # 833ns -> 542ns (53.7% faster)

def test_simple_non_palindromes():
    # Basic non-palindromic words
    codeflash_output = is_palindrome("hello") # 1.96μs -> 1.04μs (88.2% faster)
    codeflash_output = is_palindrome("python") # 1.00μs -> 625ns (60.0% faster)
    codeflash_output = is_palindrome("world") # 833ns -> 500ns (66.6% faster)
    codeflash_output = is_palindrome("palindrome") # 1.25μs -> 833ns (50.1% faster)

def test_case_insensitivity():
    # Should ignore case
    codeflash_output = is_palindrome("Madam") # 1.92μs -> 1.33μs (43.8% faster)
    codeflash_output = is_palindrome("RaceCar") # 1.21μs -> 792ns (52.7% faster)
    codeflash_output = is_palindrome("Noon") # 833ns -> 542ns (53.7% faster)

def test_ignore_non_alphanumeric():
    # Should ignore spaces, punctuation, etc.
    codeflash_output = is_palindrome("A man, a plan, a canal: Panama") # 4.21μs -> 3.25μs (29.5% faster)
    codeflash_output = is_palindrome("Was it a car or a cat I saw?") # 2.88μs -> 2.33μs (23.2% faster)
    codeflash_output = is_palindrome("Eva, can I see bees in a cave?") # 2.88μs -> 2.29μs (25.4% faster)

def test_numeric_palindromes():
    # Palindromic numbers as strings
    codeflash_output = is_palindrome("12321") # 1.96μs -> 1.42μs (38.2% faster)
    codeflash_output = is_palindrome("1221") # 917ns -> 625ns (46.7% faster)
    codeflash_output = is_palindrome("12345") # 917ns -> 583ns (57.3% faster)

def test_mixed_alphanumeric():
    # Mixed letters and numbers
    codeflash_output = is_palindrome("1abccba1") # 2.42μs -> 1.71μs (41.5% faster)
    codeflash_output = is_palindrome("1abc2cba1") # 1.62μs -> 1.17μs (39.2% faster)

# -------------------------
# EDGE TEST CASES
# -------------------------

def test_empty_string():
    # Empty string should be considered a palindrome
    codeflash_output = is_palindrome("") # 1.25μs -> 500ns (150% faster)

def test_single_character():
    # Single character is always a palindrome
    codeflash_output = is_palindrome("a") # 1.38μs -> 708ns (94.2% faster)
    codeflash_output = is_palindrome("Z") # 583ns -> 291ns (100% faster)
    codeflash_output = is_palindrome("7") # 541ns -> 291ns (85.9% faster)

def test_only_non_alphanumeric():
    # Only non-alphanumeric characters should be ignored, resulting in empty string
    codeflash_output = is_palindrome("!!!") # 1.50μs -> 792ns (89.4% faster)
    codeflash_output = is_palindrome("   ") # 667ns -> 333ns (100% faster)
    codeflash_output = is_palindrome(".") # 584ns -> 291ns (101% faster)

def test_spaces_and_punctuation():
    # Palindrome with only spaces and punctuation
    codeflash_output = is_palindrome(" , , ") # 1.42μs -> 791ns (79.1% faster)

def test_unicode_characters():
    # Unicode alphanumerics should be handled
    codeflash_output = is_palindrome("あいいあ") # 2.54μs -> 1.75μs (45.3% faster)
    codeflash_output = is_palindrome("あいえいあ") # 1.38μs -> 834ns (64.9% faster)
    codeflash_output = is_palindrome("été") # 1.04μs -> 750ns (38.9% faster)
    codeflash_output = is_palindrome("été!") # 875ns -> 583ns (50.1% faster)

def test_mixed_case_and_punctuation():
    # Mixed case and punctuation
    codeflash_output = is_palindrome("Madam, I'm Adam.") # 3.08μs -> 2.33μs (32.1% faster)
    codeflash_output = is_palindrome("No 'x' in Nixon") # 1.83μs -> 1.42μs (29.4% faster)

def test_non_palindrome_with_non_alphanumeric():
    # Non-palindrome with non-alphanumeric characters
    codeflash_output = is_palindrome("abc!def") # 2.08μs -> 1.38μs (51.5% faster)

def test_long_palindrome_with_spaces():
    # Palindrome with spaces and mixed case
    codeflash_output = is_palindrome("Able was I ere I saw Elba") # 3.79μs -> 2.92μs (30.0% faster)

def test_palindrome_with_trailing_spaces():
    # Trailing and leading spaces should be ignored
    codeflash_output = is_palindrome("  racecar  ") # 2.38μs -> 1.75μs (35.7% faster)

def test_only_numbers_and_spaces():
    # Spaces should be ignored
    codeflash_output = is_palindrome(" 12321 ") # 2.17μs -> 1.58μs (36.9% faster)

def test_non_ascii_alphanumeric():
    # Non-ASCII alphanumeric characters
    codeflash_output = is_palindrome("ßß") # 2.04μs -> 1.29μs (58.0% faster)
    codeflash_output = is_palindrome("ßaß") # 917ns -> 625ns (46.7% faster)
    codeflash_output = is_palindrome("ßabß") # 1.17μs -> 667ns (75.0% faster)

# -------------------------
# LARGE SCALE TEST CASES
# -------------------------

def test_large_palindrome():
    # Large palindrome string (1000 characters)
    half = "a" * 500
    palindrome = half + half[::-1]
    codeflash_output = is_palindrome(palindrome) # 87.0μs -> 68.9μs (26.2% faster)

def test_large_non_palindrome():
    # Large non-palindrome string (1000 characters)
    half = "a" * 500
    non_palindrome = half + "b" + half[::-1]
    codeflash_output = is_palindrome(non_palindrome) # 82.1μs -> 64.3μs (27.7% faster)

def test_large_palindrome_with_noise():
    # Large palindrome with spaces and punctuation
    half = "A" * 500
    palindrome = half + half[::-1]
    noisy_palindrome = " ".join(list(palindrome)) + "!!!"
    codeflash_output = is_palindrome(noisy_palindrome) # 98.9μs -> 81.7μs (21.1% faster)

def test_large_random_non_palindrome():
    # Large random string, not a palindrome
    import random
    import string
    s = ''.join(random.choices(string.ascii_letters + string.digits, k=1000))
    # Force non-palindrome by changing one character
    s_list = list(s)
    s_list[0] = chr(((ord(s_list[0]) + 1) % 128))
    s_mut = "".join(s_list)
    codeflash_output = is_palindrome(s_mut) # 65.4μs -> 48.0μs (36.3% faster)

def test_large_numeric_palindrome():
    # Large numeric palindrome
    half = "1234567890" * 50
    palindrome = half + half[::-1]
    codeflash_output = is_palindrome(palindrome) # 83.4μs -> 66.3μs (25.7% faster)

def test_large_palindrome_with_mixed_case_and_punctuation():
    # Large palindrome with mixed case and punctuation
    half = "AbC" * 166 + "D"
    palindrome = half + half[::-1]
    noisy_palindrome = "!@#".join(list(palindrome)).lower() + "..."
    codeflash_output = is_palindrome(noisy_palindrome) # 131μs -> 111μs (17.0% faster)

# -------------------------
# DETERMINISM TEST CASES
# -------------------------

def test_determinism():
    # The function should always return the same result for the same input
    s = "A man, a plan, a canal: Panama"
    codeflash_output = is_palindrome(s); result1 = codeflash_output # 4.08μs -> 3.17μs (29.0% faster)
    codeflash_output = is_palindrome(s); result2 = codeflash_output # 2.79μs -> 2.12μs (31.4% faster)

# -------------------------
# ADDITIONAL EDGE CASES
# -------------------------

def test_long_string_all_non_alphanumeric():
    # Long string with only non-alphanumeric characters
    s = "!" * 1000
    codeflash_output = is_palindrome(s) # 16.2μs -> 15.6μs (3.73% faster)

def test_long_string_one_alphanumeric():
    # Long string with one alphanumeric character
    s = "!" * 999 + "a"
    codeflash_output = is_palindrome(s) # 16.2μs -> 15.6μs (4.27% faster)

def test_long_string_two_different_alphanumeric():
    # Long string with two different alphanumeric characters
    s = "!" * 998 + "a" + "b"
    codeflash_output = is_palindrome(s) # 16.7μs -> 15.8μs (5.81% faster)

def test_palindrome_with_newlines_and_tabs():
    # Should ignore newlines and tabs
    codeflash_output = is_palindrome("a\nb\tb\na") # 2.12μs -> 1.46μs (45.7% faster)

def test_palindrome_with_mixed_whitespace():
    # Should ignore all whitespace
    codeflash_output = is_palindrome("a b\tc\nc\tb a") # 2.21μs -> 1.62μs (35.9% faster)

def test_non_palindrome_with_mixed_whitespace():
    codeflash_output = is_palindrome("a b\tc\nx\tb a") # 2.25μs -> 1.62μs (38.5% 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('\x00\x1f¶Ίȩ')

def test_is_palindrome_2():
    is_palindrome('')

🔎 Concolic Coverage Tests and Runtime

Test File::Test Function	Original ⏱️	Optimized ⏱️	Speedup
codeflash_concolic_fb1xiyqb/tmpltqn4_tf/test_concolic_coverage.py::test_is_palindrome	2.42μs	1.33μs	81.2%✅
codeflash_concolic_fb1xiyqb/tmpltqn4_tf/test_concolic_coverage.py::test_is_palindrome_2	1.25μs	542ns	131%✅

To edit these changes git checkout codeflash/optimize-is_palindrome-mha80huk and push.