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Palindrome Greedy

Table of Contents

409. Longest Palindrome

"""
-   Return the length of the longest palindrome that can be built with the characters in the string.
"""


def longestPalindrome(s: str) -> int:
    hashmap = dict()
    result = 0

    for char in s:
        if char not in hashmap or hashmap[char] == 0:
            hashmap[char] = 1
        else:
            result += 2
            hashmap[char] = 0

    if any(hashmap.values()):
        result += 1

    return result


print(longestPalindrome("abccccdd"))  # 7

2697. Lexicographically Smallest Palindrome

def makeSmallestPalindrome(s: str) -> str:
    n = len(s)
    s = list(s)
    left, right = 0, n - 1

    while left < right:
        if s[left] < s[right]:
            s[right] = s[left]
        elif s[left] > s[right]:
            s[left] = s[right]
        left += 1
        right -= 1

    return "".join(s)


s = "egcfe"
print(makeSmallestPalindrome(s))  # "efcfe"

680. Valid Palindrome II

1328. Break a Palindrome

# Greedy
def breakPalindrome(palindrome: str) -> str:
    n = len(palindrome)
    if n == 1:
        return ""

    for i in range(n // 2):
        if palindrome[i] != "a":
            return palindrome[:i] + "a" + palindrome[i + 1 :]

    return palindrome[:-1] + "b"


palindrome = "abccba"
print(breakPalindrome(palindrome))  # "aaccba"

1400. Construct K Palindrome Strings

from collections import Counter


def canConstructCounter(s: str, k: int) -> bool:
    if len(s) < k:
        return False

    counts = Counter(s)
    odd = 0

    for c in counts.values():
        odd += c % 2

    return odd <= k


def canConstructHash(s: str, k: int) -> bool:
    if len(s) < k:
        return False

    counts = [0 for _ in range(26)]

    for ch in s:
        idx = ord(ch) - ord("a")
        if counts[idx] == 0:
            counts[idx] += 1
        else:
            counts[idx] -= 1

    return sum(counts) <= k


s = "annabelle"
k = 2
print(canConstructCounter(s, k))  # True
print(canConstructHash(s, k))  # True

2131. Longest Palindrome by Concatenating Two Letter Words

2384. Largest Palindromic Number

3035. Maximum Palindromes After Operations

  • LeetCode | 力扣

  • Tags: Array, Hash Table, String, Greedy, Sorting, Counting

1616. Split Two Strings to Make Palindrome

1147. Longest Chunked Palindrome Decomposition

  • LeetCode | 力扣

  • Tags: Two Pointers, String, Dynamic Programming, Greedy, Rolling Hash, Hash Function

2193. Minimum Number of Moves to Make Palindrome

  • LeetCode | 力扣

  • Tags: Two Pointers, String, Greedy, Binary Indexed Tree

564. Find the Closest Palindrome

266. Palindrome Permutation 👑

from collections import defaultdict


# Hash
def canPermutePalindromeDict(s: str) -> bool:
    if len(s) == 1:
        return True

    count = defaultdict(int)

    for ch in s:
        if count[ch] == 1:
            count[ch] = 0
            continue
        count[ch] = 1

    return sum(count.values()) <= 1


# Set
def canPermutePalindromeSet(s: str) -> bool:
    if len(s) == 1:
        return True

    seen = set()

    for ch in s:
        if ch in seen:
            seen.remove(ch)
        else:
            seen.add(ch)

    return len(seen) <= 1


assert canPermutePalindromeDict("carerac") is True
assert canPermutePalindromeSet("carerac") is True

2422. Merge Operations to Turn Array Into a Palindrome 👑

1842. Next Palindrome Using Same Digits 👑

3088. Make String Anti-palindrome 👑