foo.cc: In function 'void TreeDP(int, int)':
foo.cc:58:8: warning: operation on 'len' may be undefined [-Wsequence-point]
    suf[--len] = suf[len + 1] + _min2;
        ^~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。