diff --git a/2019/d15/ex2/ex2.py b/2019/d15/ex2/ex2.py
new file mode 100755
index 0000000..ee99d3b
--- /dev/null
+++ b/2019/d15/ex2/ex2.py
@@ -0,0 +1,318 @@
+#!/usr/bin/env python
+
+import heapq
+import sys
+from dataclasses import dataclass, field
+from enum import Enum, IntEnum, auto
+from typing import List, NamedTuple, Optional, Set
+
+
+class ParameterMode(IntEnum):
+    POSITION = 0  # Acts on address
+    IMMEDIATE = 1  # Acts on the immediate value
+    RELATIVE = 2  # Acts on offset to relative base
+
+
+class Instruction(NamedTuple):
+    address: int  # The address of the instruction, for convenience
+    op: int  # The opcode
+    p1_mode: ParameterMode  # Which mode is the first parameter in
+    p2_mode: ParameterMode  # Which mode is the second parameter in
+    p3_mode: ParameterMode  # Which mode is the third parameter in
+
+
+def lookup_ops(index: int, memory: List[int]) -> Instruction:
+    digits = list(map(int, str(memory[index])))
+    a, b, c, d, e = [0] * (5 - len(digits)) + digits  # Pad with default values
+    return Instruction(
+        address=index,
+        op=d * 10 + e,
+        p1_mode=ParameterMode(c),
+        p2_mode=ParameterMode(b),
+        p3_mode=ParameterMode(a),
+    )
+
+
+class InputInterrupt(Exception):
+    pass
+
+
+class OutputInterrupt(Exception):
+    pass
+
+
+@dataclass
+class Computer:
+    memory: List[int]  # Memory space
+    rip: int = 0  # Instruction pointer
+    input_list: List[int] = field(default_factory=list)
+    output_list: List[int] = field(default_factory=list)
+    is_halted: bool = field(default=False, init=False)
+    relative_base: int = field(default=0, init=False)
+
+    def run(self) -> None:
+        while not self.is_halted:
+            self.run_single()
+
+    def run_no_output_interrupt(self) -> None:
+        while not self.is_halted:
+            try:
+                self.run_single()
+            except OutputInterrupt:
+                continue
+
+    def run_single(self):  # Returns True when halted
+        instr = lookup_ops(self.rip, self.memory)
+        if instr.op == 99:  # Halt
+            self.is_halted = True
+        elif instr.op == 1:  # Sum
+            self._do_addition(instr)
+        elif instr.op == 2:  # Multiplication
+            self._do_multiplication(instr)
+        elif instr.op == 3:  # Load from input
+            self._do_input(instr)
+        elif instr.op == 4:  # Store to output
+            self._do_output(instr)
+        elif instr.op == 5:  # Jump if true
+            self._do_jump_if_true(instr)
+        elif instr.op == 6:  # Jump if false
+            self._do_jump_if_false(instr)
+        elif instr.op == 7:  # Less than
+            self._do_less_than(instr)
+        elif instr.op == 8:  # Equal to
+            self._do_equal_to(instr)
+        elif instr.op == 9:  # Change relative base
+            self._do_change_relative_base(instr)
+        else:
+            assert False  # Sanity check
+
+    def _fill_to_addres(self, address: int) -> None:
+        values = address - len(self.memory) + 1
+        if values <= 0:
+            return
+        for __ in range(values):
+            self.memory.append(0)
+
+    def _get_value(self, mode: ParameterMode, val: int) -> int:
+        if mode == ParameterMode.POSITION:
+            assert 0 <= val  # Sanity check
+            self._fill_to_addres(val)
+            return self.memory[val]
+        elif mode == ParameterMode.RELATIVE:
+            val += self.relative_base
+            assert 0 <= val  # Sanity check
+            self._fill_to_addres(val)
+            return self.memory[val]
+        assert mode == ParameterMode.IMMEDIATE  # Sanity check
+        return val
+
+    def _set_value(self, mode: ParameterMode, address: int, value: int) -> None:
+        if mode == ParameterMode.RELATIVE:
+            address += self.relative_base
+        else:
+            assert mode == ParameterMode.POSITION  # Sanity check
+
+        assert address >= 0  # Sanity check
+        self._fill_to_addres(address)
+
+        self.memory[address] = value
+
+    def _do_addition(self, instr: Instruction) -> None:
+        lhs = self._get_value(instr.p1_mode, self.memory[instr.address + 1])
+        rhs = self._get_value(instr.p2_mode, self.memory[instr.address + 2])
+        dest = self.memory[instr.address + 3]
+
+        self._set_value(instr.p3_mode, dest, lhs + rhs)
+
+        self.rip += 4  # Length of the instruction
+
+    def _do_multiplication(self, instr: Instruction) -> None:
+        lhs = self._get_value(instr.p1_mode, self.memory[instr.address + 1])
+        rhs = self._get_value(instr.p2_mode, self.memory[instr.address + 2])
+        dest = self.memory[instr.address + 3]
+
+        self._set_value(instr.p3_mode, dest, lhs * rhs)
+
+        self.rip += 4  # Length of the instruction
+
+    def _do_input(self, instr: Instruction) -> None:
+        if len(self.input_list) == 0:
+            raise InputInterrupt  # No input, halt until an input is provided
+
+        value = int(self.input_list.pop(0))
+        param = self.memory[instr.address + 1]
+
+        self._set_value(instr.p1_mode, param, value)
+
+        self.rip += 2  # Length of the instruction
+
+    def _do_output(self, instr: Instruction) -> None:
+        value = self._get_value(instr.p1_mode, self.memory[instr.address + 1])
+
+        self.output_list.append(value)
+
+        self.rip += 2  # Length of the instruction
+        raise OutputInterrupt  # Alert that we got an output to give
+
+    def _do_jump_if_true(self, instr: Instruction) -> None:
+        cond = self._get_value(instr.p1_mode, self.memory[instr.address + 1])
+        value = self._get_value(instr.p2_mode, self.memory[instr.address + 2])
+
+        if cond != 0:
+            self.rip = value
+        else:
+            self.rip += 3  # Length of the instruction
+
+    def _do_jump_if_false(self, instr: Instruction) -> None:
+        cond = self._get_value(instr.p1_mode, self.memory[instr.address + 1])
+        value = self._get_value(instr.p2_mode, self.memory[instr.address + 2])
+
+        if cond == 0:
+            self.rip = value
+        else:
+            self.rip += 3  # Length of the instruction
+
+    def _do_less_than(self, instr: Instruction) -> None:
+        lhs = self._get_value(instr.p1_mode, self.memory[instr.address + 1])
+        rhs = self._get_value(instr.p2_mode, self.memory[instr.address + 2])
+        dest = self.memory[instr.address + 3]
+
+        self._set_value(instr.p3_mode, dest, 1 if lhs < rhs else 0)
+
+        self.rip += 4  # Length of the instruction
+
+    def _do_equal_to(self, instr: Instruction) -> None:
+        lhs = self._get_value(instr.p1_mode, self.memory[instr.address + 1])
+        rhs = self._get_value(instr.p2_mode, self.memory[instr.address + 2])
+        dest = self.memory[instr.address + 3]
+
+        self._set_value(instr.p3_mode, dest, 1 if lhs == rhs else 0)
+
+        self.rip += 4  # Length of the instruction
+
+    def _do_change_relative_base(self, instr: Instruction) -> None:
+        value = self._get_value(instr.p1_mode, self.memory[instr.address + 1])
+
+        self.relative_base += value
+        self.rip += 2  # Length of the instruction
+
+
+class Movement(IntEnum):
+    NORTH = 1
+    SOUTH = 2
+    WEST = 3
+    EAST = 4
+
+
+class StatusCode(IntEnum):
+    BLOCKED = 0
+    SUCCESS = 1
+    ON_TANK = 2
+
+
+class BlockType(Enum):
+    WALL = auto()
+    HALLWAY = auto()
+    OXYGEN_TANK = auto()
+
+
+class Coordinate(NamedTuple):
+    x: int
+    y: int
+
+
+@dataclass
+class GraphNode:
+    memory_state: Optional[List[int]]  # Only walls have no need for the memory state
+    block_type: BlockType
+    parent: Optional[Coordinate]  # Only the root of the exploration has no parent
+
+
+def coord_plus_dir(c: Coordinate, d: Movement) -> Coordinate:
+    offset = {
+        Movement.NORTH: Coordinate(0, 1),
+        Movement.SOUTH: Coordinate(0, -1),
+        Movement.WEST: Coordinate(-1, 0),
+        Movement.EAST: Coordinate(1, 0),
+    }
+    return Coordinate(*(a + b for (a, b) in zip(c, offset[d])))
+
+
+def move_to_opposite(d: Movement) -> Movement:
+    if d == Movement.NORTH:
+        return Movement.SOUTH
+    elif d == Movement.SOUTH:
+        return Movement.NORTH
+    elif d == Movement.WEST:
+        return Movement.EAST
+    else:
+        return Movement.WEST
+
+
+def main() -> None:
+    memory = [int(n) for n in sys.stdin.read().split(",")]
+    droid = Computer(memory)
+    block_map = {Coordinate(0, 0): BlockType.HALLWAY}
+
+    def dfs(p: Coordinate, direction: Movement) -> None:
+        end_coord = coord_plus_dir(p, direction)
+        if end_coord in block_map:
+            return  # Nothing to do
+
+        droid.input_list.append(int(direction))
+        try:
+            droid.run()
+        except OutputInterrupt:
+            status = StatusCode(droid.output_list.pop(0))
+            if status == StatusCode.BLOCKED:
+                block_map[end_coord] = BlockType.WALL
+                return  # Don't need to backtrack
+            block_map[end_coord] = (
+                BlockType.OXYGEN_TANK
+                if status == StatusCode.ON_TANK
+                else BlockType.HALLWAY
+            )
+            for d in Movement:
+                dfs(end_coord, d)
+            droid.input_list.append(int(move_to_opposite(direction)))
+            try:
+                droid.run()
+            except OutputInterrupt:
+                droid.output_list.pop(0)
+
+    for direction in Movement:
+        dfs(Coordinate(0, 0), direction)
+    assert len(droid.input_list) == 0 and len(droid.output_list) == 0  # Sanity check
+
+    block_map = {p: t for p, t in block_map.items() if t != BlockType.WALL}
+    oxygen_gen = (
+        pos for pos, block in block_map.items() if block == BlockType.OXYGEN_TANK
+    )
+    oxygen_pos = next(oxygen_gen)
+    assert next(oxygen_gen, None) is None  # Sanity check
+
+    seen: Set[Coordinate] = set()
+    to_visit = [(0, oxygen_pos)]
+
+    max_dist = 0
+
+    def fill_oxygen() -> None:
+        nonlocal max_dist
+        while len(to_visit) != 0:
+            dist, pos = heapq.heappop(to_visit)
+            if pos in seen:
+                continue
+            if pos not in block_map:
+                continue
+            seen.add(pos)
+            max_dist = max(max_dist, dist)
+            for d in Movement:
+                new_pos = coord_plus_dir(pos, d)
+                heapq.heappush(to_visit, (dist + 1, new_pos))
+
+    fill_oxygen()
+    print(max_dist)
+
+
+if __name__ == "__main__":
+    main()