added sum_of_all_numbers solution

beginner/sum_of_all_numbers_presleywong.py

@@ -0,0 +1,13 @@
+def sum_all(input_list):
+    if type(input_list) is not list:
+       return
+
+    total = 0
+    input_list.sort()
+    start = input_list[0]
+    end = input_list[-1]+1
+
+    for n in range(start, end):
+        total += n
+
+    return total