support fps problems import; fix qduoj problems import

problem/utils.py

@@ -1,5 +1,17 @@
 import re
 
+TEMPLATE_BASE = """//PREPEND BEGIN
+{}
+//PREPEND END
+
+//TEMPLATE BEGIN
+{}
+//TEMPLATE END
+
+//APPEND BEGIN
+{}
+//APPEND END"""
+
 
 def parse_problem_template(template_str):
     prepend = re.findall("//PREPEND BEGIN\n([\s\S]+?)//PREPEND END", template_str)
@@ -8,3 +20,7 @@ def parse_problem_template(template_str):
     return {"prepend": prepend[0] if prepend else "",
             "template": template[0] if template else "",
             "append": append[0] if append else ""}
+
+
+def build_problem_template(prepend, template, append):
+    return TEMPLATE_BASE.format(prepend, template, append)