Finish Day 2

odin/day02/day02.odin

@@ -37,13 +37,31 @@ determine_score :: proc(friendly: Move, enemy: Move) -> int {
     return result + int(friendly)
 }
 
-determine_score_alt :: proc(friendly: Move, outcome: Move) -> int {
-    // X = lose round
-    // Y = draw round
-    // Z = win round
-    // 3 defeats 2, 2 defeats 1, 1 defeats 3
-    // If w := enemy input and v := friendly input, then w = (v - 1) % 2 is a defeat
-    return 0
+/// Scoring for Part 2 of the puzzle
+determine_score_alt :: proc(outcome: Move, enemy: Move) -> int {
+    // Redefine the outcomes so that
+    // draw = 0, win = 1, lose = 2
+    outcome_ : int;
+    switch outcome {
+        // X = lose
+        case .ROCK:
+            outcome_ = 2
+        // Y = draw
+        case .PAPER:
+            outcome_ = 0
+        // Z = win
+        case .SCISSORS:
+            outcome_ = 1
+    }
+    // Convert enemy from range [1, 3] to range [0, 2]
+    enemy_ := int(enemy) - 1
+    // Assert that (friendly - enemy = outcome) % 3 (see scratch.py)
+    // Thus, (friendly = outcome + enemy) % 3
+    friendly_ := (outcome_ + enemy_) % 3
+    // Add 1 back in because we subtracted it before (going from [0, 2] to [1, 3])
+    friendly_ = friendly_ + 1
+    // Return score as before
+    return determine_score(cast(Move)friendly_, enemy)
 }
 
 main :: proc () {
@@ -56,7 +74,7 @@ main :: proc () {
     fh, errno := os.open(os.args[1])
     if errno != os.ERROR_NONE {
         fmt.printf("Cannot open %s: %s\n", os.args[1], os.get_last_error_string())
-        os.exit(int(errno))
+        os.exit(-1)
     }
     defer os.close(fh)
 
@@ -64,6 +82,7 @@ main :: proc () {
     defer delete(buffer);
 
     num_read, error := os.read(fh, buffer)
+    score : int = 0;
     total_score : int = 0;
     friendly : Move
     enemy : Move
@@ -73,8 +92,9 @@ main :: proc () {
         chr = buffer[0]
         switch chr {
             case '\n':
-            fmt.printf("Score for this line: %d\n", determine_score(friendly, enemy))
-            total_score += determine_score(friendly, enemy)
+            score = determine_score_alt(friendly, enemy)
+            fmt.printf("Score for this line: %d\n", score)
+            total_score += score
             case 'A':
                 enemy = .ROCK
             case 'B':
@@ -92,7 +112,7 @@ main :: proc () {
         }
     }
     if chr != '\n' {
-        total_score += determine_score(friendly, enemy)
+        total_score += determine_score_alt(friendly, enemy)
     }
     /// Handle potential errors
     if error != os.ERROR_NONE {