2022: Day 2 complete

2022/2.c

@@ -0,0 +1,117 @@
+#include <stdio.h>
+#include <string.h>
+
+struct RPS_Game {
+  // Part 1 Rock / Part 2 Lose
+  const int X;
+  // Part 1 Paper / Part 2 Draw
+  const int Y;
+  // Part 1 Scissors / Part 2 Win
+  const int Z;
+  // Outcomes
+  const int draw;
+  const int win;
+};
+
+// Part 1 - Calculate score
+void process_round(struct RPS_Game *game, int *score, const char opponent_move,
+                   const char my_move) {
+
+  switch (my_move) {
+  case 'X': // Rock
+    *score += game->X;
+    if (opponent_move == 'A') {
+      *score += game->draw;
+    } else if (opponent_move == 'C') {
+      *score += game->win;
+    }
+    break;
+  case 'Y': // Paper
+    *score += game->Y;
+    if (opponent_move == 'A') {
+      *score += game->win;
+    } else if (opponent_move == 'B') {
+      *score += game->draw;
+    }
+    break;
+  case 'Z': // Scissors
+    *score += game->Z;
+    if (opponent_move == 'B') {
+      *score += game->win;
+    } else if (opponent_move == 'C') {
+      *score += game->draw;
+    }
+    break;
+  }
+}
+
+// Part 2 - Find move given a desired result, then calculate score
+void find_move(struct RPS_Game *game, int *score, const char opponent_move,
+               const char result) {
+
+  char my_move = '\0';
+
+  switch (result) {
+  case 'X': // need to lose
+    if (opponent_move == 'A') {
+      my_move = 'Z';
+    } else if (opponent_move == 'B') {
+      my_move = 'X';
+    } else if (opponent_move == 'C') {
+      my_move = 'Y';
+    }
+    break;
+  case 'Y': // need a draw
+    if (opponent_move == 'A') {
+      my_move = 'X';
+    } else if (opponent_move == 'B') {
+      my_move = 'Y';
+    } else if (opponent_move == 'C') {
+      my_move = 'Z';
+    }
+    break;
+  case 'Z': // need to win
+    if (opponent_move == 'A') {
+      my_move = 'Y';
+    } else if (opponent_move == 'B') {
+      my_move = 'Z';
+    } else if (opponent_move == 'C') {
+      my_move = 'X';
+    }
+    break;
+  }
+  process_round(game, score, opponent_move, my_move);
+}
+
+int main(int argc, char *argv[]) {
+
+  if (argc != 2) {
+    fprintf(stderr, "USAGE: %s input_file\n", argv[0]);
+    return 1;
+  }
+
+  FILE *file = fopen(argv[1], "r");
+  if (!file) {
+    fprintf(stderr, "Error opening file %s\n", argv[1]);
+    return 1;
+  }
+
+  int part1_score = 0;
+  int part2_score = 0;
+  char round[5] = {0};
+  struct RPS_Game game = {.X = 1, .Y = 2, .Z = 3, .draw = 3, .win = 6};
+
+  while (fgets(round, sizeof round / sizeof *round, file) != NULL) {
+    if (strlen(round) == 1) {
+      break;
+    }
+    process_round(&game, &part1_score, round[0], round[2]);
+    find_move(&game, &part2_score, round[0], round[2]);
+  }
+
+  fclose(file);
+  printf("My part 1 score: %d\n", part1_score);
+  printf("My part 2 score: %d\n", part2_score);
+
+  return 0;
+}