From 6961baf4416bec288b9d3438a182fc35d68a3186 Mon Sep 17 00:00:00 2001
From: Dimitri Lozeve <dimitri@lozeve.com>
Date: Thu, 1 Apr 2021 19:44:38 +0200
Subject: [PATCH] Add solution for March 2021

---
 202103/grid.txt | 20 ++++++++++++++++++++
 202103/rover.jl | 41 +++++++++++++++++++++++++++++++++++++++++
 202103/test.txt |  4 ++++
 3 files changed, 65 insertions(+)
 create mode 100644 202103/grid.txt
 create mode 100644 202103/rover.jl
 create mode 100644 202103/test.txt

diff --git a/202103/grid.txt b/202103/grid.txt
new file mode 100644
index 0000000..09c814c
--- /dev/null
+++ b/202103/grid.txt
@@ -0,0 +1,20 @@
+BC E6 56 29 99 95 AE 27 9F 89 88 8F BC B4 2A 71 44 7F AF 96
+72 57 13 DD 08 44 9E A0 13 09 3F D5 AA 06 5E DB E1 EF 14 0B
+42 B8 F3 8E 58 F0 FA 7F 7C BD FF AF DB D9 13 3E 5D D4 30 FB
+60 CA B4 A1 73 E4 31 B5 B3 0C 85 DD 27 42 4F D0 11 09 28 39
+1B 40 7C B1 01 79 52 53 65 65 BE 0F 4A 43 CD D7 A6 FE 7F 51
+25 AB CC 20 F9 CC 7F 3B 4F 22 9C 72 F5 FE F9 BF A5 58 1F C7
+EA B2 E4 F8 72 7B 80 A2 D7 C1 4F 46 D1 5E FA AB 12 40 82 7E
+52 BF 4D 37 C6 5F 3D EF 56 11 D2 69 A4 02 0D 58 11 A7 9E 06
+F6 B2 60 AF 83 08 4E 11 71 27 60 6F 9E 0A D3 19 20 F6 A3 40
+B7 26 1B 3A 18 FE E3 3C FB DA 7E 78 CA 49 F3 FE 14 86 53 E9
+1A 19 54 BD 1A 55 20 3B 59 42 8C 07 BA C5 27 A6 31 87 2A E2
+36 82 E0 14 B6 09 C9 F5 57 5B 16 1A FA 1C 8A B2 DB F2 41 52
+87 AC 9F CC 65 0A 4C 6F 87 FD 30 7D B4 FA CB 6D 03 64 CD 19
+DC 22 FB B1 32 98 75 62 EF 1A 14 DC 5E 0A A2 ED 12 B5 CA C0
+05 BE F3 1F CB B7 8A 8F 62 BA 11 12 A0 F6 79 FC 4D 97 74 4A
+3C B9 0A 92 5E 8A DD A6 09 FF 68 82 F2 EE 9F 17 D2 D5 5C 72
+76 CD 8D 05 61 BB 41 94 F9 FD 5C 72 71 21 54 3F 3B 32 E6 8F
+45 3F 00 43 BB 07 1D 85 FC E2 24 CE 76 2C 96 40 10 FB 64 88
+FB 89 D1 E3 81 0C E1 4C 37 B2 1D 60 40 D1 A5 2D 3B E4 85 87
+E5 D7 05 D7 7D 9C C9 F5 70 0B 17 7B EF 18 83 46 79 0D 49 59
diff --git a/202103/rover.jl b/202103/rover.jl
new file mode 100644
index 0000000..1af8800
--- /dev/null
+++ b/202103/rover.jl
@@ -0,0 +1,41 @@
+# https://www.research.ibm.com/haifa/ponderthis/challenges/March2021.html
+
+using DelimitedFiles
+using JuMP, GLPK
+
+function readgrid(filename)
+    open(filename) do f
+        parse.(Int, readdlm(f, String); base=16) .- 128
+    end
+end
+
+function optimalset(grid)
+    n = size(grid, 1)
+    model = Model(GLPK.Optimizer)
+    @variable(model, x[1:n, 1:n], Bin)
+    for i = 2:n, j = 1:n
+        if j > 1
+            @constraint(model, x[i, j] <= x[i-1, j-1])
+        end
+        @constraint(model, x[i, j] <= x[i-1, j])
+        if j < n
+            @constraint(model, x[i, j] <= x[i-1, j+1])
+        end
+    end
+    @objective(model, Max, sum(grid[i, j] * x[i, j] for i = 1:n, j = 1:n))
+
+    optimize!(model)
+    obj = Int(objective_value(model))
+    indices = Tuple.(findall(value.(x) .> 0))
+    indices = sort([(a-1, b-1) for (a, b) = indices])
+    obj, indices
+end
+
+if !isinteractive()
+    for filename = ["test.txt", "grid.txt"]
+        grid = readgrid(filename)
+        obj, indices = optimalset(grid)
+        println(obj)
+        println(indices)
+    end
+end
diff --git a/202103/test.txt b/202103/test.txt
new file mode 100644
index 0000000..c2a150a
--- /dev/null
+++ b/202103/test.txt
@@ -0,0 +1,4 @@
+13 92 49 EC
+BD 31 E8 FF
+09 DD BE DE
+C9 5A 1D 36