From 93f1c73fbf56dd670c4693c60ebe6a61ddeda858 Mon Sep 17 00:00:00 2001
From: Max Nuding <max.nuding@icloud.com>
Date: Thu, 9 Dec 2021 20:01:26 +0100
Subject: [PATCH] Caching neighbours

---
 Sources/09/09.swift | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/Sources/09/09.swift b/Sources/09/09.swift
index 18fe9bd..055cf8c 100644
--- a/Sources/09/09.swift
+++ b/Sources/09/09.swift
@@ -38,6 +38,8 @@ struct Field:Sequence, IteratorProtocol {
     let numCols: Int
     let numRows: Int
     
+    var neighbors = [Coord:[Coord]]()
+    
     var current: Coord? = Coord(row: 0, col: 0)
     
     init(numbers: [[Int]]) {
@@ -46,13 +48,15 @@ struct Field:Sequence, IteratorProtocol {
         numRows = numbers.count
     }
     
-    func getNeighborsCoordsFor(coord: Coord) -> [Coord] {
-        return [coord.getAbove(), coord.getRight(), coord.getBelow(), coord.getLeft()]
+    mutating func getNeighborsCoordsFor(coord: Coord) -> [Coord] {
+        let n = neighbors[coord] ?? [coord.getAbove(), coord.getRight(), coord.getBelow(), coord.getLeft()]
             .compactMap { $0 }
             .filter { $0.row < numRows && $0.col < numCols }
+        neighbors[coord] = n
+        return n
     }
     
-    func isLowPointAt(coord: Coord) -> Bool {
+    mutating func isLowPointAt(coord: Coord) -> Bool {
         let value = self[coord]
         return getNeighborsCoordsFor(coord: coord)
             .map { numbers[$0.row][$0.col] }