最大回文子串

package chengxu;

public class wodezuidahuiwen {

public static void main(String[] args) {
String s="babcbabcbaccba";
String result=findmaxhuiwen(s);
System.out.println(result);

}

private static String findmaxhuiwen(String s) {
int start=0;
int len=s.length();
int changdu=0;
//若字符串长度为单数
for(int i=0;i<s.length();i++){
int pre=i-1;int end=i+1;
while(pre>0&&end<len&&s.charAt(pre)==s.charAt(end)){

if(end-pre+1>changdu){
changdu=end-pre+1;
start=pre;
}
pre--;
end++;
}

}
//若字符串长度为偶数
for(int j=0;j<s.length();j++){
int pre=j;int end=j+1;
while(pre>0&&end<len&&s.charAt(pre)==s.charAt(end)){

if(end-pre+1>changdu){
changdu=end-pre+1;
start=pre;
}
pre--;
end++;
}

}
if(changdu>0)
return s.substring(start,changdu+1);
return null;
}

}