day 5 awk solution

day05/sol.awk

@@ -0,0 +1,58 @@
+# run me with awk -f sol.awk < input
+
+/\[/ {
+    gsub("^   ", "[ ]")
+    gsub(" {4}", " [ ]")
+    gsub("^\\[|\\] \\[|\\]$", "")
+    lines[nlines++] = $0
+    if (nstacks < length())
+        nstacks = length()
+}
+
+/^$/ {
+    for (i = 1; i <= nstacks; i++) {
+        s = ""
+        for (j = nlines-1; j >= 0; j--) {
+            c = substr(lines[j], i, 1)
+            if (c != " ") s = s c
+        }
+        stack[i] = s
+        stack2[i] = s
+        print s "."
+    }
+    print "----"
+}
+
+function reverse(s) {
+    r = ""
+    for (i = length(s); i > 0; i--)
+        r = r substr(s, i, 1)
+    return r
+}
+
+function move(S, n, fr, to, flip) {
+    #print n, fr, to
+    m = length(S[fr]) - n
+    if (flip) chunk = reverse(substr(S[fr], m+1))
+    else      chunk =         substr(S[fr], m+1)
+    #print stack[to]
+    #print stack[fr]
+    S[to] = S[to] chunk
+    S[fr] = substr(S[fr], 1, m)
+    #print stack[to]
+    #print stack[fr]
+}
+
+/^move .* from .* to .*/  {
+    move(stack, $2, $4, $6, 0)
+    move(stack2, $2, $4, $6, 1)
+}
+
+END {
+    for (i = 1; i <= nstacks; i++) {
+        p1 = p1 substr(stack[i], length(stack[i]))
+        p2 = p2 substr(stack2[i], length(stack2[i]))
+    }
+    print p1
+    print p2
+}