Simplifica algoritmo de mo

fontes/mo.h

 vector<int> mo(vector<qry> qs) {
   vector<int> ans (qs.size());
   sort(qs.begin(), qs.end(), [](qry a, qry b) {
-    if (a.l/B != b.l/B)
-      return make_pair(a.l, a.r) < make_pair(b.l, b.r);
+    if (a.l/B != b.l/B) { return a.l < b.l; }
     return (a.l/B) % 2 ? a.r < b.r : a.r > b.r;
   });
   int l = 0, r = -1;