力扣第五题

每次都从尾部开始从前找，如果当前所找的位置大于max，才判别当前字符串是否为回文串，如果是更新max，break

class Solution {
    public String longestPalindrome(String s) {
        if(s==null||s.length()<1){
            return"";
        }
        int start=0,end=0;
        for(int i=0;i<s.length();i++){
            int len1=strandCenter(s,i,i);
            int len2=strandCenter(s,i,i+1);
            int len = Math.max(len1,len2);
            if(len>end-start){
                start=i-(len-1)/2;
                end=i+len/2;
            }
        }
        return s.substring(start,end+1);
    }
    public int strandCenter(String s,int left,int right){
        while(left>=0&&right<s.length()&&s.charAt(left)==s.charAt(right)){
            left--;
            right++;
        }
        return right-left-1;
    }
}