/in/foo.cc: In function 'void kruskal(int, int)':
/in/foo.cc:74:45: warning: suggest parentheses around comparison in operand of '!=' [-Wparentheses]
   if(day[j][u][v]-day[i-1][u][v]!=0||find(u)==find(v)!=0) continue;
                                      ~~~~~~~^~~~~~~~~