day 5 awk add some comments

day05/sol.awk

@@ -1,15 +1,17 @@
 # run me with awk -f sol.awk < input
 
-/\[/ {
-    gsub("^   ", "[ ]")
-    gsub(" {4}", " [ ]")
-    gsub("^\\[|\\] \\[|\\]$", "")
+/\[/ {                            # "    [A]     [B] [C]    "
+    gsub("^   ", "[ ]")           # "[ ] [A]     [B] [C]    "
+    gsub(" {4}", " [ ]")          # "[ ] [A] [ ] [B] [C] [ ]"
+    gsub("^\\[|\\] \\[|\\]$", "") # " A BC "
     lines[nlines++] = $0
     if (nstacks < length())
         nstacks = length()
 }
 
 /^$/ {
+    # transpose lines[j][i] -> stack[i][-j]
+    # and strip trailing spaces
     for (i = 1; i <= nstacks; i++) {
         s = ""
         for (j = nlines-1; j >= 0; j--) {