> For the complete documentation index, see [llms.txt](https://jenhsuan.gitbook.io/algorithm/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jenhsuan.gitbook.io/algorithm/leetcode/409.-longest-palindrome-easy.md).

# 409. Longest Palindrome (Easy)

## 1.問題

* 給予一個由大小寫字母組成的string, 找出可以組成的最長迴文字串

![](/files/-LI-OU67NPQuY3QX_HIc)

## 2.想法 

* 統計每個字母出現的次數
  * 出現一次者
  * 出現兩次者
* 將字元轉為int來統計

```
vector<int> sv(59, 0);
for(int i = 0 ; i < (int)s.size(); i++){
        sv[(int)(s[i] - 'A')]++;
}
```

## 3.程式碼

```
class Solution {
public:
    int longestPalindrome(string s) {
        vector<int> sv(59, 0);
        for(int i = 0 ; i < (int)s.size(); i++){
            sv[(int)(s[i] - 'A')]++;
        }
        int pairCount = 0;
        int singleCount = 0;
        for(int i = 0 ; i < 59; i++){
            while(sv[i] != 0 && sv[i] != 1 ){
                sv[i] = sv[i] - 2;
                pairCount += 2;
            }
            if(sv[i] == 1){
                singleCount++;
            }
        }
        return singleCount > 0 ? pairCount + 1 : pairCount;
    }
};
```

## 4.Performance

![](/files/-LI-PUiiTD-sliiAogkw)