回文子串长度

  	  var len = s.length;
      var begin = 0;
      var maxLen = 1;
      if (len == 1) return s;
      for (var i = 0; i < len; i++) {
        for (var j = len - 1; j > i; j--) {
          if (j - i + 1 > maxLen && verify(s, i, j)) {
            maxLen = j - i + 1;
            begin = i;
          }
        }
      }
      //判断当前字符串是否为回文串
      function verify(str, start, end) {
        while (start < end) {
          if (str[start] != str[end]) {
            return false;
          }
          start++;
          end--;
        }
        return true;
      }
      return s.substr(begin, maxLen);