day 9!

12023/09/09.lua

@@ -0,0 +1,47 @@
+io.input("input")
+
+sum1 = 0
+sum2 = 0
+for line in io.lines() do
+    seq = {}
+    for num in line:gmatch("%-*%d+") do -- THE SIGN!
+        table.insert(seq,tonumber(num))
+    end
+    len = #seq
+    seqs = {}
+    table.insert(seqs, seq)
+    --print(table.concat(seq,", "))
+    ptr = 1
+    diffs = {}
+    repeat
+        all0 = true
+        curr = seqs[ptr]
+        nseq = {}
+        --print(ptr)
+        for i=ptr+1,len do
+            nseq[i] = curr[i]-curr[i-1]
+            if nseq[i]~= 0 then all0 = false end
+            --print(i,curr[i], curr[i-1], "->", nseq[i])
+        end
+        table.insert(seqs, nseq)
+        ptr = ptr+1 
+    until all0
+    nextnum = 0
+    for i=#seqs,1,-1 do
+        nextnum = nextnum + seqs[i][len]
+    end
+    sum1 = sum1 + nextnum
+    --print("next:",nextnum)
+    
+    -- part 2
+    prevnum = 0
+    for i=1,#seqs do
+        n = seqs[i][i]
+        prevnum = (i%2==0) and (prevnum-n) or prevnum+n
+    end
+    --print("prev:",prevnum)
+    sum2 = sum2 + prevnum
+end
+
+print("part 1", sum1)
+print("part 2", sum2)

12023/09/test

@@ -0,0 +1,3 @@
+0 3 6 9 12 15
+1 3 6 10 15 21
+10 13 16 21 30 45