From 08a93a5418d0ccb5d5c2697123878d6591b38844 Mon Sep 17 00:00:00 2001
From: Bryce Allen <bdallen@uchicago.edu>
Date: Fri, 17 Dec 2021 16:54:37 -0500
Subject: [PATCH] day15 p2 performance

Getting rid of the temp neighbor vector allocation is major speedup
---
 day15/part2.jl | 31 ++++++++++++++-----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/day15/part2.jl b/day15/part2.jl
index 208a1ac..9e8635a 100755
--- a/day15/part2.jl
+++ b/day15/part2.jl
@@ -154,30 +154,27 @@ risk_map = tile_map(risk_map)
 #println()
 #exit()
 
-function neighbor_idx(nrows, ncols, y, x)
-    v = CartesianIndex[]
-    if x > 1
-        push!(v, CartesianIndex(y, x-1))
+function relax(nrows, ncols, R, costs, row, col; first=false)
+    c1 = costs[row, col]
+    c = c1
+    if col > 1
+        c = min(c, costs[row, col-1] + R[row, col])
     end
-    if x < ncols
-        push!(v, CartesianIndex(y, x+1))
+    if col < ncols
+        c = min(c, costs[row, col+1] + R[row, col])
     end
-    if y > 1
-        push!(v, CartesianIndex(y-1, x))
+    if row > 1
+        c = min(c, costs[row-1, col] + R[row, col])
     end
-    if y < nrows
-        push!(v, CartesianIndex(y+1, x))
+    if row < nrows
+        c = min(c, costs[row+1, col] + R[row, col])
     end
-    return v
-end
 
-function relax(nrows, ncols, R, costs, row, col; first=false)
-    idx = neighbor_idx(nrows, ncols, row, col)
-    c = minimum(costs[i] for i in idx) + R[row, col]
-    if first || c < costs[row, col]
+    if c < c1
         costs[row, col] = c
         return true
     end
+
     return false
 end
 
@@ -233,7 +230,7 @@ function get_costs(R)
     return costs, dirs
 end
 
-costs, dirs = get_costs(risk_map)
+@time costs, dirs = get_costs(risk_map)
 
 if length(costs) < 1000
     display(costs)