day21

3 files changed, 67 insertions, 0 deletions

diff --git a/2021/day21/day21 b/2021/day21/day21
new file mode 100755
index 0000000..5fa0bb4
--- /dev/null
+++ b/2021/day21/day21
diff --git a/2021/day21/day21.cpp b/2021/day21/day21.cpp
new file mode 100644
index 0000000..b1b764c
--- /dev/null
+++ b/2021/day21/day21.cpp
@@ -0,0 +1,65 @@
+#include <iostream>
+#include <string>
+
+long long winp = 0, winq = 0;
+
+void stepseq (int p, int q, int sp, int sq, int turn, int roll, int die) {
+	if (turn == 0) {
+		if (roll < 3) {
+			stepseq((p+die)%10, q, sp, sq, turn, roll+1, die+1);
+		} else {
+			int score = p==0 ? sp+10 : sp+p;
+			if (score >= 1000) std::cout << "win sq*die: " << sq*(die-1) << std::endl;
+			else stepseq(p, q, score, sq, (turn+1)%2, 0, die);
+		}
+	}
+	if (turn == 1) {
+		if (roll < 3) {
+			stepseq(p, (q+die)%10, sp, sq, turn, roll+1, die+1);
+		} else {
+			int score = q==0 ? sq+10 : sq+q;
+			if (score >= 1000) std::cout << "win sp*die: " << sp*(die-1) << std::endl;
+			else stepseq(p, q, sp, score, (turn+1)%2, 0, die);
+		}
+	}
+}
+
+void step (int p, int q, int sp, int sq, int turn, long mul) {
+	//std::cout << p<<" "<<q<< " "<<sp << " " <<sq << ",,,, "<<turn<<" "<<mul<<std::endl;
+	int incp = p==0 ? 10 : p;
+	int incq = q==0 ? 10 : q;
+	if (sp+incp >= 21) { winp += mul; return; }
+	if (sq+incq >= 21) { winq += mul; return; }
+	if (turn % 2 == 0) {
+		int score = sp+incp;
+		if (turn == 0) score = 0;
+		step((p+3)%10, q, score, sq, turn+1, mul*1);
+		step((p+4)%10, q, score, sq, turn+1, mul*3);
+		step((p+5)%10, q, score, sq, turn+1, mul*6);
+		step((p+6)%10, q, score, sq, turn+1, mul*7);
+		step((p+7)%10, q, score, sq, turn+1, mul*6);
+		step((p+8)%10, q, score, sq, turn+1, mul*3);
+		step((p+9)%10, q, score, sq, turn+1, mul*1);
+	}
+	if (turn % 2 == 1) {
+		int score = sq+incq;
+		if (turn == 1) score = 0;
+		step(p, (q+3)%10, sp, score, turn+1, mul*1);
+		step(p, (q+4)%10, sp, score, turn+1, mul*3);
+		step(p, (q+5)%10, sp, score, turn+1, mul*6);
+		step(p, (q+6)%10, sp, score, turn+1, mul*7);
+		step(p, (q+7)%10, sp, score, turn+1, mul*6);
+		step(p, (q+8)%10, sp, score, turn+1, mul*3);
+		step(p, (q+9)%10, sp, score, turn+1, mul*1);
+	}
+}
+
+int main (int argc, char *argv[]) {
+	int p = std::stoi(std::string{ argv[1] });
+	int q = std::stoi(std::string{ argv[2] });
+	stepseq(p, q, 0, 0, 0, 0, 1);
+	step(p, q, 0, 0, 0, 1);
+	std::cout << "wins " << winp << " " << winq << std::endl;
+
+	return 0;
+}
diff --git a/2021/day21/makefile b/2021/day21/makefile
new file mode 100644
index 0000000..512e963
--- /dev/null
+++ b/2021/day21/makefile
@@ -0,0 +1,2 @@
+all day21:
+	g++ -std=c++20 day21.cpp -o day21