已自行解决，将
```
ret.dat = max(max(ll.dat, rr.dat), ll.rm + rr.lm);
```
改为
```
ret.sum = ll.sum + rr.sum;
ret.dat = max(max(ll.dat, rr.dat), ll.rm + rr.lm);
ret.lm = max(ll.lm, rr.lm + ll.sum);
ret.rm = max(rr.rm, rr.sum + ll.rm);
```
即 AC。
by ReeChee @ 2022-09-08 07:37:45