i finally undestood dijkstra's algorithm!!!

examples/aoc2024/day16/part1.jou

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+import "stdlib/io.jou"
+import "stdlib/str.jou"
+import "stdlib/math.jou"
+import "stdlib/mem.jou"
+import "../../aoc2023/grid.jou"
+
+
+class State:
+    place: int[2]
+    direction: int[2]
+    score: int
+
+    def next_states(self) -> State[3]:
+        x = self->place[0]
+        y = self->place[1]
+        dx = self->direction[0]
+        dy = self->direction[1]
+
+        return [
+            # Go forward
+            State{place=[x+dx, y+dy], direction=[dx, dy], score=self->score + 1},
+            # Turn both ways
+            #State{place=[x, y], direction=[-dy, dx], score=self->score + 1000},
+            #State{place=[x, y], direction=[dy, -dx], score=self->score + 1000},
+            State{place=[x, y], direction=[-dy, dx], score=self->score + 1},
+            State{place=[x, y], direction=[dy, -dx], score=self->score + 1},
+        ]
+
+
+def direction_to_0123(dir: int[2]) -> int:
+    if dir[0] == 1 and dir[1] == 0:
+        return 0  # right
+    if dir[0] == 0 and dir[1] == 1:
+        return 1  # down
+    if dir[0] == -1 and dir[1] == 0:
+        return 2  # left
+    if dir[0] == 0 and dir[1] == -1:
+        return 3  # up
+    assert False
+
+declare usleep(x: int) -> int
+def main() -> int:
+    f = fopen("input", "r")
+    assert f != NULL
+    grid = read_grid_from_file(f)
+    fclose(f)
+
+    int_max = 0x7fffffff  # TODO: belongs to stdlib
+
+    assert grid.width <= 150
+    assert grid.height <= 150
+    smallest_scores: int[4][150][150]* = malloc(sizeof(*smallest_scores))
+    assert smallest_scores != NULL
+
+    # (*smallest_scores)[x][y][direction as 0123] = shortest path to x,y counting turns
+    for x = 0; x < grid.width; x++:
+        for y = 0; y < grid.height; y++:
+            (*smallest_scores)[x][y] = [int_max, int_max, int_max, int_max]
+
+    todo: State[1000]
+    todo[0] = State{place = grid.find_first('S'), direction = [1, 0]}
+    todo_len = 1
+    while todo_len > 0:
+        # Pop from front (fast enough because todo list is short)
+        state = todo[0]
+        todo_len--
+        memmove(&todo[0], &todo[1], todo_len * sizeof(todo[0]))
+#        state = todo[--todo_len]
+
+        scoreptr = &(*smallest_scores)[state.place[0]][state.place[1]][direction_to_0123(state.direction)]
+
+        # Ignore states that have ran into walls.
+        if grid.get(state.place) == '#':
+            continue
+
+        # Ignore this state if some other todo list item has already reached
+        # the same place with a better score. That other todo list item will do
+        # a better job when discovering other paths.
+        if state.score < *scoreptr:
+            *scoreptr = state.score
+            next_states: State[3] = state.next_states()
+            assert todo_len + 3 <= sizeof(todo)/sizeof(todo[0])
+            memcpy(&todo[todo_len], &next_states, sizeof(next_states))
+            todo_len += 3
+
+        for y = 0; y < grid.height; y++:
+            for x = 0; x < grid.width; x++:
+                in_todo = False
+                for i = 0; i < todo_len; i++:
+                    if todo[i].place[0] == x and todo[i].place[1] == y:
+                        in_todo = True
+                if in_todo:
+                    printf("\x1b[1;44m")  # ANSI code for yellow
+
+                if grid.get([x, y]) == '#':
+                    putchar('#')
+                else:
+                    best = min(
+                        min(
+                            (*smallest_scores)[x][y][0],
+                            (*smallest_scores)[x][y][1],
+                        ),
+                        min(
+                            (*smallest_scores)[x][y][2],
+                            (*smallest_scores)[x][y][3],
+                        )
+                    )
+                    s = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+                    if best >= strlen(s):
+                        putchar('.')
+                    else:
+                        putchar(s[best])
+
+                if in_todo:
+                    printf("\x1b[1;0m")  # ANSI code reset
+            putchar('\n')
+
+        printf("\n\n\n")
+        fflush(stdout)
+        usleep(30000)
+
+    pos = grid.find_first('E')
+    printf("%d %d %d %d\n",
+        (*smallest_scores)[pos[0]][pos[1]][0],
+        (*smallest_scores)[pos[0]][pos[1]][1],
+        (*smallest_scores)[pos[0]][pos[1]][2],
+        (*smallest_scores)[pos[0]][pos[1]][3],
+    )
+
+    return 0

examples/aoc2024/day16/sampleinput.txt

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+###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############