From 6267bb6dd9d6871a2df14dfad30087cb68b9f045 Mon Sep 17 00:00:00 2001
From: Christopher Arndt <chris@chrisarndt.de>
Date: Sun, 3 Dec 2023 13:33:19 +0100
Subject: [PATCH] Day 03 part two

Signed-off-by: Christopher Arndt <chris@chrisarndt.de>
---
 day_03/solution_03.nim  | 39 +++++++++---------
 day_03/solution_03b.nim | 87 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+), 19 deletions(-)
 create mode 100644 day_03/solution_03b.nim

diff --git a/day_03/solution_03.nim b/day_03/solution_03.nim
index d2f7c4a..3d249ec 100644
--- a/day_03/solution_03.nim
+++ b/day_03/solution_03.nim
@@ -1,18 +1,6 @@
-import std/[cmdline, sequtils, strformat, strutils]
+import std/[cmdline, sequtils, strformat, strutils, sugar]
 
-var fn: string
-
-if paramCount() > 0:
-    fn = paramStr(1)
-else:
-    fn = "input_03.txt"
-
-var result = 0
-var lines = readFile(fn).strip.splitLines
-var grid = newSeqWith(lines.len, newSeq[char](lines[0].strip.len))
-
-
-proc isAdjacentToSymbol(row, col: int): bool =
+proc isAdjacentToCond(grid: seq[seq[char]], row, col: int, cond: (char) -> bool): bool =
     for i in @[row - 1, row, row + 1]:
         if i < 0 or i >= grid.len:
             continue
@@ -22,11 +10,17 @@ proc isAdjacentToSymbol(row, col: int): bool =
             if j < 0 or j >= grid[i].len:
                 continue
             var ch = grid[i][j]
-            if not ch.isDigit and ch != '.':
+            if cond(ch):
                 return true
     return false
 
 
+var fn = if paramCount() > 0: paramStr(1) else: "input_03.txt"
+
+var result = 0
+var lines = readFile(fn).strip.splitLines
+var grid = newSeqWith(lines.len, newSeq[char](lines[0].strip.len))
+
 for i, line in lines:
     for j, ch in line.strip:
         grid[i][j] = ch
@@ -41,19 +35,26 @@ for i, row in grid:
     for j, ch in row:
         if ch.isDigit:
             number &= ch
-            if isAdjacentToSymbol(i, j):
+            if isAdjacentToCond(grid, i, j, (c) => not c.isDigit and c != '.'):
                 isPartNumber = true
         else:
             if isPartNumber:
                 #echo number.parseInt
                 result += number.parseInt
-            elif number.len > 0:
-                echo &"Not a part number: {number.parseInt} (row {i}, col {j})"
+            #elif number.len > 0:
+            #    echo &"Not a part number: {number.parseInt} (row {i}, col {j})"
+
             number = ""
             isPartNumber = false
 
-    # account for numbers going untl the end of the row
+    # account for numbers going until the end of the row
     if isPartNumber:
         result += number.parseInt
 
 echo &"Result: {result}"
+
+case fn:
+    of "input_03.txt":
+        assert result == 559667
+    of "sample_input_03.txt":
+        assert result == 4361
diff --git a/day_03/solution_03b.nim b/day_03/solution_03b.nim
new file mode 100644
index 0000000..12013ba
--- /dev/null
+++ b/day_03/solution_03b.nim
@@ -0,0 +1,87 @@
+import std/[cmdline, sequtils, strformat, strutils, sugar, tables]
+
+type Position = tuple
+    row: int
+    col: int
+
+## Check if any of the grid cells adjacent to position (i, j) match condition cond.
+proc isAdjacentToCond(grid: seq[seq[char]], row, col: int, cond: (char) -> bool): Position =
+    for i in @[row - 1, row, row + 1]:
+        if i < 0 or i >= grid.len:
+            continue
+        for j in @[col - 1, col, col + 1]:
+            if i == row and j == col:
+                continue
+            if j < 0 or j >= grid[i].len:
+                continue
+            var ch = grid[i][j]
+            if cond(ch):
+                return (i, j)
+    return (-1, -1)
+
+
+var fn = if paramCount() > 0: paramStr(1) else: "input_03.txt"
+var result = 0
+# read input file as seq of lines
+var lines = readFile(fn).strip.splitLines
+# allocate 2-D seq to hold ros and colums of characters
+var grid = newSeqWith(lines.len, newSeq[char](lines[0].strip.len))
+# table to save positions of gears and parts connected to it
+var gears = initTable[Position, seq[int]]()
+
+# Parse input
+for i, line in lines:
+    for j, ch in line.strip:
+        grid[i][j] = ch
+
+#echo &"Rows: {grid.len}"
+#echo &"Cols: {grid[0].len}"
+
+# Go through grid and find positions of gears
+for i, row in grid:
+    var
+        isConnectedToGear = false
+        gear: Position
+        number = ""
+
+    for j, ch in row:
+        if ch.isDigit:
+            number &= ch
+            # Scan adjacent grid cells gor a gear ('*')
+            var symbol = isAdjacentToCond(grid, i, j, (c) => c == '*')
+
+            if symbol != (-1, -1):
+                # It's a number adjacent to a gear!
+                isConnectedToGear = true
+                gear = symbol
+                if not gears.hasKey(gear):
+                    # save gear position in table
+                    gears[gear] = newSeq[int]()
+        else:
+            if isConnectedToGear:
+                # add part to gear position saved above
+                # we can save an infinite amount of parts per gear
+                # but we assume that at most two parts are connected to a gear
+                gears[gear].add(number.parseInt)
+
+            number = ""
+            isConnectedToGear = false
+
+    # account for numbers going until the end of the row
+    if isConnectedToGear:
+        # add part to gear position saved above
+        gears[gear].add(number.parseInt)
+
+# Sum up gear ratios
+for pos, parts in gears:
+    # Ignore gears conencted to only one part
+    if parts.len > 1:
+        result += parts[0] * parts[1]
+
+echo &"Result: {result}"
+
+case fn:
+    of "input_03.txt":
+        assert result == 86841457
+    of "sample_input_03.txt":
+        assert result == 467835