update: slice exercises 21, 23, 24, 25, 26

16-slices/exercises/24-fix-the-memory-leak/hints.md

@@ -0,0 +1,16 @@
+# Hints
+
++ `millions` slice's backing array uses 65 MB of memory.
+
++ `make` a new slice with 10 elements with a new backing array.
+
+  + `copy` the last 10 elements of the `millions` slice to the new slice.
+
+  + So you will have slice with a new backing array only with 10 elements.
+
+  + Then overwrite the `millions` slice by simply `assigning` `last10` slice to it.
+
++ **Remember:** slice ~= pointer to a backing array.
+
+  If you overwrite the slice, it will lose that
+  pointer. So Go can collect the unused memory.