Perserverance, or the lack thereof

commit cbd3c63584bd7d7bb68db69deabd59368afc2700
parent c3fc2b38859fe28f21c7c8c196340262c39ed935
Author: Shimmy Xu <shimmy.xu@shimmy1996.com>
Date:   Mon, 16 Dec 2019 09:40:18 -0500

Add Julia solution for day 16

Diffstat:
 A day-16/Makefile | 9 +++++++++ A day-16/day-16.jl | 47 +++++++++++++++++++++++++++++++++++++++++++++++ A day-16/input.txt | 1 +
3 files changed, 57 insertions(+), 0 deletions(-)
diff --git a/day-16/Makefile b/day-16/Makefile
@@ -0,0 +1,9 @@
+CC := g++
+CCFLAGS := --std=c++17 -Wall
+
+all: day-16-rust day-16.jl
+	julia day-16.jl
+	./day-16-rust
+
+day-16-rust: day-16.rs
+	rustc \$^ -o \$@
diff --git a/day-16/day-16.jl b/day-16/day-16.jl
@@ -0,0 +1,47 @@
+function fft!(signal)
+    pattern = [0, 1, 0, -1]
+    for i in 1:length(signal)
+        curr_signal = 0
+        for j in i:length(signal)
+            curr_signal += pattern[j ÷ i % length(pattern) + 1] * signal[j]
+        end
+        signal[i] = abs(curr_signal) % 10
+    end
+end
+
+function digits_to_num(digits)
+    num = 0
+    for i in 1:length(digits)
+        num = num * 10 + digits[i]
+    end
+    num
+end
+
+function part_1(input)
+    signal = copy(input)
+    for _ in 1:100
+        fft!(signal)
+    end
+    digits_to_num(signal[1:8])
+end
+
+function part_2(input)
+    offset = digits_to_num(input[1:7])
+    # We only care about signal beyond the offset.
+    signal = repeat(input, 10000)[offset:end]
+    # Since this will be in latter half of the signal, the only pattern we see
+    # is i 0s and (n - i) 1s.
+    for _ in 1:100
+        reverse!(signal)
+        cumsum!(signal, signal, dims = 1)
+        reverse!(signal)
+        signal .%= 10
+    end
+    digits_to_num(signal[2:9])
+end
+
+input = map(x -> parse(Int, x), collect(readlines(open("input.txt"))[1]))
+
+println("Julia:")
+println("Part 1: ", part_1(input))
+println("Part 2: ", part_2(input))
diff --git a/day-16/input.txt b/day-16/input.txt
@@ -0,0 +1 @@
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