/in/foo.cc: In function 'void chuli1(int)':
/in/foo.cc:140:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < pre[pos - 1].size(); i++)
                     ~~^~~~~~~~~~~~~~~~~~~~~
/in/foo.cc: In function 'void chuli2(int)':
/in/foo.cc:225:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < last[pos + 1].size(); i++)
                     ~~^~~~~~~~~~~~~~~~~~~~~~
/in/foo.cc: In function 'void solve(int, int)':
/in/foo.cc:363:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < pre[pos1].size(); i++)
                     ~~^~~~~~~~~~~~~~~~~~
/in/foo.cc:365:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < last[pos2].size(); i++)
                     ~~^~~~~~~~~~~~~~~~~~~