Longest Palindrome(leetcode409)

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.

//天然想到的正向思惟 偶數的數量確定能夠組成迴文，奇數只要獲取其中的偶數個 若是能夠中間還能夠放一個
public static int longestPalindrome(String s) {

    int result = 0;
    Map<Character,Integer> map = new HashMap<>();
    for (int i =0;i<s.length();i++){
        if(map.containsKey(s.charAt(i))){
             Integer count = map.get(s.charAt(i));
             count ++;
             map.put(s.charAt(i),count);
        }else{
            map.put(s.charAt(i),1);
        }
    }
    int jishu =0;
    for (Map.Entry<Character, Integer> entry : map.entrySet()) {
        if(entry.getValue()%2==0){
            result+=entry.getValue();
        }else{
            result = entry.getValue()+result-1;
            jishu++;
        }
    }
    if(jishu> 0){
        result++;
    }

    return result;
}

//這個加加減減的方式 也是能夠的
public static int longestPalindrome2(String s) {
    if(s==null || s.length()==0) {
        return 0;
    }
    HashSet<Character> hs = new HashSet<Character>();
    int count = 0;
    for(int i=0; i<s.length(); i++){
        if(hs.contains(s.charAt(i))){
            hs.remove(s.charAt(i));
            count++;
        }else{
            hs.add(s.charAt(i));
        }
    }
    if(!hs.isEmpty()) {
        return count*2+1;
    }
    return count*2;
}

//這裏用整型數量的特性 除以2乘以2  就沒有奇數偶數的問題
public static int longestPalindrome3(String s) {
    int[] lowercase = new int[26];
    int[] uppercase = new int[26];
    int res = 0;
    for (int i = 0; i < s.length(); i++){
        char temp = s.charAt(i);
        if (temp >= 97) {
            lowercase[temp-'a']++;
        } else {
            uppercase[temp-'A']++;
        }
    }
    for (int i = 0; i < 26; i++){
        res+=(lowercase[i]/2)*2;
        res+=(uppercase[i]/2)*2;
    }
    return res == s.length() ? res : res+1;

}

//與上面的不一樣  這是獲取奇數的數量
public static int longestPalindrome4(String s) {
    int[] chars = new int[128];
    char[] t = s.toCharArray();
    for(char c:t){
        chars[c]++;
    }
    int single = 0;
    for(int n:chars){
        if(n%2!=0){
            single++;
        }
    }
    return single>1?t.length-single+1:t.length;
}

git:https://github.com/woshiyexinjie/leetcode-xin