# Deadlock and Optimizations

## Deadlock detections
### Simple corner deadlock detection
The simple corner deadlock that was already implemented aims to prevent a box
from being pushed into a corner. If it is pushed into a corner, it is
inaccessible and immovable, thus rendering that state unsolvable.

### Freeze deadlock detection
Described 
[here](http://sokobano.de/wiki/index.php?title=Deadlocks#Freeze_deadlocks), 
freeze detection is about preventing two boxes from being adjacent against a 
wall when there is no goal in that location. This deadlock detection was chosen
as there are many scenarios (such as in test_maps/test_map2 and 
test_maps/test_map3) where there are multiple boxes and a complex map layout.
This deadlock detection saves a small amount time and reduces the number of 
nodes that are expanded.

The code for this detection is contained in `utils.c`, from lines 321 - 480. 
The function `freeze_deadlock()` is used to check if there is a box adjacent to
the player, and if there is, then the function `adjacent_box_check()` is called
to check for the freeze deadlock scenario.

## Optimisation results
These results show the impact of implementing the freeze deadlock detection.

Hardware used:
- CPU: AMD Ryzen 4800U
- GPU: AMD Radeon RX Vega 8
- Memory: 16GB

### Summary of optimisation
The following table summarises some of the key statistics prior to implementing
freeze deadlock detection, and after implementing freeze deadlock detection.

Test: test_map1

| Statistic      | Before implementation | After implementation | % improvement |
|----------------|-----------------------|----------------------|---------------|
| Expanded nodes | 13                    | 13                   | 0.00          |
| Time (s)       | 0.050106              | 0.047723             | 4.76          |


Test: test_map2

| Statistic      | Before implementation | After implementation | % improvement |
|----------------|-----------------------|----------------------|---------------|
| Expanded nodes | 978745                | 944140               | 3.54          |
| Time           | 3.456764              | 3.227685             | 6.63          |

Test: test_map3

| Statistic      | Before implementation | After implementation | % improvement |
|----------------|-----------------------|----------------------|---------------|
| Expanded nodes | 230041                | 215253               | 6.43          |
| Time           | 1.828733              | 1.680901             | 8.08          |

### Full output (before optimisation)
```
$ ./sokoban -s test_maps/test_map1

SOLUTION:
rrRRRR

STATS:
	Expanded nodes: 13
	Generated nodes: 48
	Duplicated nodes: 8
	Solution Length: 6
	Expanded/seconds: 259
	Time (seconds): 0.050106

$ ./sokoban -s test_maps/test_map2

SOLUTION:
rrrrrrdrdLLLLLLLLullluRRRRRRRururRRRRRRRRRR

STATS:
	Expanded nodes: 978745
	Generated nodes: 3914976
	Duplicated nodes: 2288345
	Solution Length: 43
	Expanded/seconds: 283139
	Time (seconds): 3.456764

$ ./sokoban -s test_maps/test_map3

SOLUTION:
drdrdrdrrruuuuuulllllddrdrdrDulululldRdRdrdRRllululuurdrdrDululldRuuluurrrrrdddddrddlUUUUUUruLLLLLulDDdrdddrdRRlluluurdrDulldruluulldRuuurrrrrdddddrddlUUUUUUruLLLLLulDDdrdrdddRRlluurDldRuulululldRdRluuuurrrrrdddddrddlUUUUUUruLLLLLulDDdrdrdrddRluulululldRdRluuuurrrrrdddddrddlUUUUUUruLLLLLulDD

STATS:
	Expanded nodes: 230041
	Generated nodes: 920160
	Duplicated nodes: 331571
	Solution Length: 292
	Expanded/seconds: 125792
	Time (seconds): 1.828733
```

### Full output (after optimisation)
```
$ ./sokoban -s test_maps/test_map1

SOLUTION:
rrRRRR

STATS:
	Expanded nodes: 13
	Generated nodes: 48
	Duplicated nodes: 8
	Solution Length: 6
	Expanded/seconds: 272
	Time (seconds): 0.047723

$ ./sokoban -s test_maps/test_map2

SOLUTION:
rrrrrrdrdLLLLLLLLullluRRRRRRRurruRRRRRRRRRR

STATS:
	Expanded nodes: 944140
	Generated nodes: 3776556
	Duplicated nodes: 2199712
	Solution Length: 43
	Expanded/seconds: 292513
	Time (seconds): 3.227685

$ ./sokoban -s test_maps/test_map3

SOLUTION:
drdrdrdrrruuuuuulllllddrdrdrDulululldRdRdrdRRllululuurdrdrDululldRuuluurrrrrdddddrddlUUUUUUruLLLLLulDDdrdddrdRRlluluurdrDulldruululldRuuurrrrrdddddrddlUUUUUUruLLLLLulDDdrdrdddRRlluurDldRluuululldRdRluuuurrrrrdddddrddlUUUUUUruLLLLLulDDdrdrdrddRluulululldRdRluuuurrrrrdddddrddlUUUUUUruLLLLLulDD

STATS:
	Expanded nodes: 215253
	Generated nodes: 861008
	Duplicated nodes: 309654
	Solution Length: 292
	Expanded/seconds: 128058
	Time (seconds): 1.680901
```