advent2019

commit dbe8221ce0b2c9672dc92ef833e240bc0b821d16
parent 1abca040b7e39f5ab2f8fc5799071195442d866e
Author: bsandro <email@bsandro.tech>
Date:   Sun,  7 Dec 2025 01:44:27 +0200

Day 02

Diffstat:
A
day02.c
 | 
83
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 83 insertions(+), 0 deletions(-)
diff --git a/day02.c b/day02.c
@@ -0,0 +1,83 @@
+#include <stdio.h>
+#include <inttypes.h>
+#include <string.h>
+
+#define MAX_LEN 256
+
+typedef struct {
+    char data[16];
+    int len;
+} Buffer;
+
+typedef int Program[MAX_LEN];
+
+int btoi(Buffer buf) {
+    int num = 0;
+    for (int i=0;i<buf.len;++i) num = num*10+buf.data[i];
+    return num;
+}
+
+void program_print(const Program prg) {
+    for (int i=0;i<MAX_LEN;++i) {
+        printf("%d,", prg[i]);
+    }
+    printf("\n");
+}
+
+int program_step(Program prg, int ip) {
+    int opcode = prg[ip];
+    switch (opcode) {
+    case 1: { // addition
+        prg[prg[ip+3]] = prg[prg[ip+1]] + prg[prg[ip+2]];
+        return ip+4;
+    }
+    case 2: { // multiplication
+        prg[prg[ip+3]] = prg[prg[ip+1]] * prg[prg[ip+2]];
+        return ip+4;
+    }
+    case 99: return -1; // halt
+    }
+    return -2;
+}
+
+int program_run(const Program prg1, int noun, int verb) {
+    Program prg = {0};
+    memcpy(prg, prg1, MAX_LEN*sizeof(prg[0]));
+    int ip = 0;
+    prg[1] = noun;
+    prg[2] = verb;
+    for (ip=0; ip!=-1&&ip<MAX_LEN; ip=program_step(prg, ip)) {
+        if (ip==-2) {
+            printf("invalid opcode\n");
+            return 0;
+        }
+    }
+    return prg[0];
+}
+
+int main(void) {
+    Program prg = {0};
+    int ip = 0;
+    Buffer buf = {0};
+    for (int c=getchar();c!=EOF;c=getchar()) {
+        if (c>='0'&&c<='9') {
+            buf.data[buf.len++] = c-'0';
+        } else {
+            prg[ip++] = btoi(buf);
+            buf.len = 0;
+        }
+    }
+    int p1 = program_run(prg, 12, 2);
+    int p2 = 0;
+    for (int noun=0; noun<100; ++noun) {
+        for (int verb=0; verb<100; ++verb) {
+            if (program_run(prg, noun, verb) == 19690720) {
+                p2 = 100*noun+verb;
+                goto fin;
+            }
+        }
+    }
+    fin:
+    printf("p1: %d\np2: %d\n", p1, p2);
+    return 0;
+}