sort samples by max length of source and target sequences

source/sample/transformer/T2TTrainer.cpp

@@ -557,9 +557,12 @@ int T2TTrainer::LoadBuf(FILE * file, bool isSorted, int step)
             node.offset = i;
             node.p = buf + offset;
             node.size = 0;
-            for(int j = 0; j < step; j++)
+            int max = 0;
+            for (int j = 0; j < step; j++) {
                 node.size += seqLen[i + j];
-            node.value = seqLen[i];
+                max = MAX(max, seqLen[i + j]);
+            }
+            node.value = max;
             node.key = rand();
             count++;
             offset += node.size;