PAT甲级-1040 Longest Symmetric String (25分)【推荐！！！】

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题目：
Given a string, you are supposed to output the length of the longest symmetric sub-string. For example, given Is PAT&TAP symmetric?, the longest symmetric sub-string is s PAT&TAP s, hence you must output 11.

Input Specification:
Each input file contains one test case which gives a non-empty string of length no more than 1000.

Output Specification:
For each test case, simply print the maximum length in a line.

Sample Input:

Is PAT&TAP symmetric?

Sample Output:

11

题意：
找字符串最长回文子串的长度

我的思路：
找到某个可能成为回文的中心的点，计算从他出发，两边多少长度都是一样的。
注意： 回文的中心可能是一个点，也可能是两个点

我的代码：

#include
using namespace std;
string str;
int fun(int left,int right,int len){
    if(str[left]!=str[right]||left<0||right>=str.length())return len;
    return fun(left-1,right+1,len+2);
}
int main()
{
    getline(cin,str);
    int max_len=1;
    for(int i=0;i<str.length();i++)
    {
        if(str[i]==str[i+1])max_len=max(max_len,fun(i,i+1,0));
        if(str[i]==str[i+2])max_len=max(max_len,fun(i,i+2,1));
    }
    cout<<max_len<<endl;

    return 0;
}