Day9

day9/rope.c

@@ -0,0 +1,129 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define BUFFER_SIZE 64
+#define MAX_LOG 16*1024
+#define FOLLOW_LENGTH 1
+#define ROPE_LENGTH 10
+
+void logTailPosition(int, int, int (**)[2]);
+void move(char, int*);
+void follow(int*, int*, int*);
+
+int main() {
+    char buf[BUFFER_SIZE], *p, c;
+    memset(buf, 0, BUFFER_SIZE);
+    p = buf;
+    int moveCount;
+    // We will keep a log of the tail position just in case it is needed in the second part
+    int tailLog[MAX_LOG][2];
+    memset(tailLog, 0, MAX_LOG * sizeof(int[2]));
+    int (*tailLogHead)[2] = tailLog;
+
+
+    // Relative to the start pos
+    int ropePos[ROPE_LENGTH][2];
+    memset(ropePos, 0, ROPE_LENGTH * sizeof(int[2]));
+    logTailPosition(0, 0, &tailLogHead);
+
+    int diff[2];
+
+    while ((c = getchar()) != EOF) {
+        *p++ = c;
+        if (c == '\n') {
+            sscanf(buf, "%c %i", &c, &moveCount);
+            for (int i = 0; i < moveCount; i++) {
+                move(c, ropePos[0]);
+                for (int j = 0; j < ROPE_LENGTH - 2; j++) {
+                    follow(diff, ropePos[j], ropePos[j+1]);    
+                    ropePos[j+1][0] += diff[0];
+                    ropePos[j+1][1] += diff[1];
+                }
+                follow(diff, ropePos[ROPE_LENGTH - 2], *(tailLogHead-1));    
+                logTailPosition((*(tailLogHead-1))[0] + diff[0], (*(tailLogHead-1))[1] + diff[1], &tailLogHead);
+            }
+
+            memset(buf, 0, BUFFER_SIZE);
+            p = buf;
+        }
+    }
+
+    // Look at log and find unique places
+    // Using a bintree would be better but its fine for now
+    int uniques[MAX_LOG][2], uniquesLength = 0;
+    for (int i = 1; i < (tailLogHead - tailLog); i++) {
+        int found = 0;
+        for (int j = 0; j < uniquesLength; j++) {
+            if (uniques[j][0] == tailLog[i][0] && uniques[j][1] == tailLog[i][1]) {
+                found = 1;
+                break;
+            }
+        }
+        if (!found) {
+            uniques[uniquesLength][0] = tailLog[i][0];
+            uniques[uniquesLength][1] = tailLog[i][1];
+            uniquesLength++;
+        }
+    }
+
+    printf("%i\n", uniquesLength);
+}
+
+void logTailPosition(int x, int y, int (**tailLogHead)[2]) {
+    (**tailLogHead)[0] = x;
+    (**tailLogHead)[1] = y;
+    *tailLogHead += 1;
+}
+
+void move(char dir, int *pos) {
+    switch (dir) {
+        case 'U':
+            pos[1]++;
+            break;
+        case 'D':
+            pos[1]--;
+            break;
+        case 'R':
+            pos[0]++;
+            break;
+        case 'L':
+            pos[0]--;
+            break;
+    }
+}
+
+void follow(int* diff, int* head, int* tail) {
+    diff[0] = 0;
+    diff[1] = 0;
+
+    if (head[0] - tail[0] > FOLLOW_LENGTH) {
+        diff[0]++;
+        if (head[1] > tail[1]) {
+            diff[1]++;
+        } else if (head[1] < tail[1]) {
+            diff[1]--;
+        }
+    } else if (tail[0] - head[0] > FOLLOW_LENGTH) {
+        diff[0]--;
+        if (head[1] > tail[1]) {
+            diff[1]++;
+        } else if (head[1] < tail[1]) {
+            diff[1]--;
+        }
+    } else if (head[1] - tail[1] > FOLLOW_LENGTH) {
+        diff[1]++;
+        if (head[0] > tail[0]) {
+            diff[0]++;
+        } else if (head[0] < tail[0]) {
+            diff[0]--;
+        }
+    } else if (tail[1] - head[1] > FOLLOW_LENGTH) {
+        diff[1]--;
+        if (head[0] > tail[0]) {
+            diff[0]++;
+        } else if (head[0] < tail[0]) {
+            diff[0]--;
+        }
+    }
+}