leetcode 409：給定字符串，求能重組成的最長迴文字符串

# -*- coding: utf-8 -*-
# @Time         : 2019-10-11 10:56
# @Author       : Jayce Wong
# @ProjectName  : job
# @FileName     : longestPalindrome.py
# @Blog         : https://blog.51cto.com/jayce1111
# @Github       : https://github.com/SysuJayce

"""
Given a string which consists of lowercase or uppercase letters, find the
length of the longest palindromes that can be built with those letters.

This is case sensitive, for example "Aa" is not considered a palindrome here.

Note:
Assume the length of given string will not exceed 1,010.

Example:

Input:
"abccccdd"

Output:
7

Explanation:
One longest palindrome that can be built is "dccaccd", whose length is 7.
"""

class Solution:
    """
    給定一個字符串，問其中的字符最多能組成多長的迴文字符串？

    其實咱們能夠這樣想，所謂的迴文字符串，就是從左到右和從右到左的遍歷是同樣的，那麼就是說，
    每一個字符都須要出現偶數次，固然，若是是奇數長度的迴文字符串，其中間的字符能夠是隻出現了一次。

    也就是說，咱們只須要判斷給定的字符串中各個字符的出現次數，把偶數次的字符挑出來，而後從奇數次的
    字符中找一個(若是存在出現次數爲奇數的字符的話)，這些字符就能組成最長的迴文字符串。
    """
    def longestPalindrome(self, s: str) -> int:
        from collections import Counter
        # 找出全部奇數次的字符
        odds = sum(v & 1 for v in Counter(s).values())
        # 先把奇數次的字符去掉，而後從中找一個(若是有)
        return len(s) - odds + bool(odds)