/in/foo.cc: In function 'int main()':
/in/foo.cc:28:41: warning: iteration 5000 invokes undefined behavior [-Waggressive-loop-optimizations]
     for (i=1;i<=5001;i++) node[i].father=i;//把并查集初始化
                           ~~~~~~~~~~~~~~^~
/in/foo.cc:28:15: note: within this loop
     for (i=1;i<=5001;i++) node[i].father=i;//把并查集初始化
              ~^~~~~~