diff --git a/examples/aoc2024/day15/part1.jou b/examples/aoc2024/day15/part1.jou
index f7fb4365..7af0f769 100644
--- a/examples/aoc2024/day15/part1.jou
+++ b/examples/aoc2024/day15/part1.jou
@@ -4,7 +4,7 @@ import "stdlib/str.jou"
 import "../../aoc2023/grid.jou"
 
 
-def move_right(grid: Grid*, start: byte*) -> None:
+def move_right(start: byte*) -> None:
     assert start != NULL
     assert *start == '@'
 
@@ -36,19 +36,19 @@ def horizontal_mirror(grid: Grid*) -> None:
 
 def move(grid: Grid*, how: byte) -> None:
     if how == '>':
-        move_right(grid, strstr(grid->data, "@"))
+        move_right(strstr(grid->data, "@"))
     elif how == 'v':
         grid->transpose()
-        move_right(grid, strstr(grid->data, "@"))
+        move_right(strstr(grid->data, "@"))
         grid->transpose()
     elif how == '<':
         horizontal_mirror(grid)
-        move_right(grid, strstr(grid->data, "@"))
+        move_right(strstr(grid->data, "@"))
         horizontal_mirror(grid)
     elif how == '^':
         grid->transpose()
         horizontal_mirror(grid)
-        move_right(grid, strstr(grid->data, "@"))
+        move_right(strstr(grid->data, "@"))
         horizontal_mirror(grid)
         grid->transpose()
     else:
@@ -56,7 +56,7 @@ def move(grid: Grid*, how: byte) -> None:
 
 
 def main() -> int:
-    f = fopen("sampleinput.txt", "r")
+    f = fopen("sampleinput1.txt", "r")
     assert f != NULL
     grid = read_grid_from_file(f)
 
diff --git a/examples/aoc2024/day15/part2.jou b/examples/aoc2024/day15/part2.jou
new file mode 100644
index 00000000..882f3d3b
--- /dev/null
+++ b/examples/aoc2024/day15/part2.jou
@@ -0,0 +1,190 @@
+import "stdlib/io.jou"
+import "stdlib/mem.jou"
+import "stdlib/str.jou"
+import "../../aoc2023/grid.jou"
+
+
+def move_right(start: byte*) -> None:
+    assert start != NULL
+    assert *start == '@'
+
+    relevant_length = strspn(start, "@.[]")
+
+    first_blank = -1
+    for i = 0; i < relevant_length; i++:
+        if start[i] == '.':
+            first_blank = i
+            break
+
+    if first_blank == -1:
+        # no room to move, do nothing
+        return
+
+    # shift boxes to the right
+    memmove(&start[2], &start[1], first_blank - 1)
+    start[0] = '.'
+    start[1] = '@'
+
+
+# x_left and y specify the location of "[" part of box
+def can_move_box_up(grid: Grid*, x: int, y: int) -> bool:
+    if grid->get([x, y]) == '[':
+        x_left = x
+        x_right = x+1
+    elif grid->get([x, y]) == ']':
+        x_left = x-1
+        x_right = x
+    else:
+        assert False
+
+    if grid->get([x_left, y-1]) == '#' or grid->get([x_right, y-1]) == '#':
+        # bumping into wall
+        return False
+
+    for x = x_left; x <= x_right; x++:
+        if strchr("[]", grid->get([x, y-1])) != NULL and not can_move_box_up(grid, x, y-1):
+            # Some kind of box (aligned or not) above, and it won't move.
+            return False
+
+    return True
+
+
+def move_box_up(grid: Grid*, x: int, y: int) -> None:
+    if grid->get([x, y]) == '[':
+        x_left = x
+        x_right = x+1
+    elif grid->get([x, y]) == ']':
+        x_left = x-1
+        x_right = x
+    else:
+        assert False
+
+    for x = x_left; x <= x_right; x++:
+        if strchr("[]", grid->get([x, y-1])) != NULL:
+            move_box_up(grid, x, y-1)
+
+    assert grid->get([x_left, y-1]) == '.'
+    assert grid->get([x_right, y-1]) == '.'
+    assert grid->get([x_left, y]) == '['
+    assert grid->get([x_right, y]) == ']'
+
+    grid->set([x_left, y-1], '[')
+    grid->set([x_right, y-1], ']')
+    grid->set([x_left, y], '.')
+    grid->set([x_right, y], '.')
+
+
+def can_move_up(grid: Grid*) -> bool:
+    pos: int[2] = grid->find_first('@')
+    above = [pos[0], pos[1] - 1]
+
+    return (
+        grid->get(above) == '.'
+        or (
+            strchr("[]", grid->get(above)) != NULL
+            and can_move_box_up(grid, above[0], above[1])
+        )
+    )
+
+
+def move_up(grid: Grid*) -> None:
+    pos: int[2] = grid->find_first('@')
+    above = [pos[0], pos[1] - 1]
+
+    if strchr("[]", grid->get(above)) != NULL:
+        move_box_up(grid, above[0], above[1])
+
+    assert grid->get(above) == '.'
+    assert grid->get(pos) == '@'
+
+    grid->set(above, '@')
+    grid->set(pos, '.')
+
+
+def horizontal_mirror(grid: Grid*) -> None:
+    bytes_per_row = grid->width + 1
+    for y = 0; y < grid->height; y++:
+        first = &grid->data[bytes_per_row * y]
+        last = &first[grid->width - 1]
+        while first < last:
+            memswap(first++, last--, 1)
+
+
+def vertical_mirror(grid: Grid*) -> None:
+    bytes_per_row = grid->width + 1
+    first = grid->data
+    last = &first[bytes_per_row*(grid->height - 1)]
+
+    while first < last:
+        memswap(first, last, grid->width)
+        first = &first[bytes_per_row]
+        last = &last[-bytes_per_row]
+
+
+def move(grid: Grid*, how: byte) -> None:
+    if how == '>':
+        move_right(strstr(grid->data, "@"))
+    elif how == '<':
+        horizontal_mirror(grid)
+        move_right(strstr(grid->data, "@"))
+        horizontal_mirror(grid)
+    elif how == '^':
+        if can_move_up(grid):
+            move_up(grid)
+    elif how == 'v':
+        vertical_mirror(grid)
+        if can_move_up(grid):
+            move_up(grid)
+        vertical_mirror(grid)
+    else:
+        assert False
+
+
+def double_width(grid: Grid*) -> None:
+    new_grid = Grid{
+        width = 2 * grid->width,
+        height = grid->height,
+        data = malloc((2*grid->width + 1)*grid->height + 1),
+    }
+    new_grid.data[0] = '\0'
+    for y = 0; y < grid->height; y++:
+        for x = 0; x < grid->width; x++:
+            if grid->get([x, y]) == 'O':
+                strcat(new_grid.data, "[]")
+            elif grid->get([x, y]) == '@':
+                strcat(new_grid.data, "@.")
+            else:
+                s = [grid->get([x, y]), grid->get([x, y]), '\0']
+                strcat(new_grid.data, s)
+        strcat(new_grid.data, "\n")
+
+    free(grid->data)
+    *grid = new_grid
+
+
+def main() -> int:
+    f = fopen("sampleinput2.txt", "r")
+    assert f != NULL
+    grid = read_grid_from_file(f)
+    double_width(&grid)
+
+    while True:
+        #getchar()
+        c = fgetc(f)
+        if c == -1:  # TODO: EOF constant
+            break
+        if c == '\n':
+            continue
+        move(&grid, c as byte)
+
+    fclose(f)
+
+    result = 0
+    for x = 0; x < grid.width; x++:
+        for y = 0; y < grid.height; y++:
+            if grid.get([x, y]) == '[':
+                result += 100*y + x
+    printf("%d\n", result)  # Output: 9021
+
+    free(grid.data)
+    return 0
diff --git a/examples/aoc2024/day15/sampleinput.txt b/examples/aoc2024/day15/sampleinput1.txt
similarity index 100%
rename from examples/aoc2024/day15/sampleinput.txt
rename to examples/aoc2024/day15/sampleinput1.txt
diff --git a/examples/aoc2024/day15/sampleinput2-simple.txt b/examples/aoc2024/day15/sampleinput2-simple.txt
new file mode 100644
index 00000000..6ee6098f
--- /dev/null
+++ b/examples/aoc2024/day15/sampleinput2-simple.txt
@@ -0,0 +1,9 @@
+#######
+#...#.#
+#.....#
+#..OO@#
+#..O..#
+#.....#
+#######
+
+<vv<<^^<<^^
diff --git a/examples/aoc2024/day15/sampleinput2.txt b/examples/aoc2024/day15/sampleinput2.txt
new file mode 100644
index 00000000..84cf1fbf
--- /dev/null
+++ b/examples/aoc2024/day15/sampleinput2.txt
@@ -0,0 +1,21 @@
+##########
+#..O..O.O#
+#......O.#
+#.OO..O.O#
+#..O@..O.#
+#O#..O...#
+#O..O..O.#
+#.OO.O.OO#
+#....O...#
+##########
+
+<vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><<><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^
+vvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<>><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v
+><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<
+<<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^<vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^
+^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>>^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><
+^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><<<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^
+>^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv<<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^
+<><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><<><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>
+^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^>vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>
+v^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v><^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^