leet-code use python3 if available

projects/leet-code/.gitignore

@@ -0,0 +1 @@
+main.py

projects/leet-code/build.hxml

@@ -3,4 +3,4 @@
 --main leet_code.Main
 -dce full
 --python main.py
--cmd python main.py
+-cmd bash test-python.sh

projects/leet-code/test-python.sh

@@ -0,0 +1,6 @@
+# "python" is supposed to mean Python3 everywhere now, but not in practice
+if [ ! -z "$(which python3)" ]; then
+    python3 main.py
+else
+    python main.py
+fi