The **Number Puzzle** (commonly known as the **Sliding Tile Puzzle** or **15-Puzzle**) is played on a grid—most commonly $3 \times 3$ (8-puzzle) or $4 \times 4$ (15-puzzle)—containing numbered tiles and one empty space.
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**1. The Goal**
Rearrange the scrambled numbered tiles in numerical order from **top-left to bottom-right**, ending with the empty space in the bottom-right corner.
* **3×3 Target Layout:**
| 1 | 2 | 3 |
| --- | --- | --- |
| **4** | **5** | **6** |
| **7** | **8** | **[ ]** |
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**2. Basic Rules**
1. **Slide, Don't Lift:** You can only move a tile into an adjacent empty space (horizontally or vertically).
2. **One at a Time:** Tiles cannot jump over other tiles.
3. **No Overlapping:** Only one tile can occupy a slot at any time.
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**3. Step-by-Step Solving Strategy**
The most effective way to solve a sliding puzzle is row-by-row, moving from top to bottom.
1. **Solve the Top Row First:**
Place **1** in the top-left corner, then **2**, and finally **3** in the top-right corner. Once the top row is complete, lock those tiles in place and do not disturb them.
2. **Solve the First Column / Middle Row:**
* For $3 \times 3$ puzzles: Position **4** in its spot under **1**.
* Slide **7** into place below **4**.
3. **Solve the Final 2x2 Corner:**
Rotate the remaining tiles (**5**, **6**, **8**, and the empty space) clockwise or counter-clockwise within the remaining $2 \times 2$ space until **5**, **6**, and **8** fall into sequence.
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**Pro Tip for Edge Tiles**
If you struggle to fit the last number in a row (e.g., getting **3** into the top-right corner):
1. Move tile **3** directly below the top-right corner.
2. Move tile **2** into the top-right corner.
3. Slide **3** up into the top-right corner, pushing **2** back into place.