Flood It is a flood fill game online that starts on an original, deterministic 5-by-5 color board and can be solved in the independently proven minimum of eight moves. Your controlled territory begins on the top-left tile, outlined so you can see its boundaries. Each move recolors that entire connected territory and absorbs any matching tiles touching it horizontally or vertically. The goal is to make all 25 tiles one color by move eight, then press Check board or Enter to receive exactly 1,000 points. Unlike a random color grid that changes from session to session, this fixture stays identical every time, so every move can be tested, undone, and audited. You can play Flood It in a browser with pointer controls or a complete keyboard setup; no account, download, or remote game service is needed. This guide explains the exact board rules, gives a playable eight-move sequence, shows how to recover from a poor choice, and clarifies when a check is harmless or when the run becomes locked.
How the Flooding Rule Works
Flood It uses four colors: Blue, Coral, Gold, and Teal. The controlled area starts as the single top-left tile, which is Blue. On each meaningful move, choose a color different from the current top-left color. Every tile in your existing controlled component changes to that color, and matching tiles immediately outside join when they share a horizontal or vertical edge. The current color’s button is disabled because choosing it would not change the board.
The first move makes the rule concrete. Selecting Coral changes the initial Blue tile and pulls in the Coral cells directly to its right and below, together with their orthogonally connected Coral neighbor. The controlled indices become 0, 1, 5, and 6. Another Coral tile elsewhere remains outside because no orthogonal path currently links it to your territory. Your region can bend around the board and eventually contain many tiles, but it always remains a connected monochromatic area with an orthogonal path back to the top-left.
- Diagonal contact never joins tiles; only shared edges establish a connection.
- Every controlled tile is outlined, so its status is visible without relying on color alone.
- Every tile carries a letter: B for Blue, C for Coral, G for Gold, and T for Teal.
Play the Verified Eight-Move Route
- Open the linked Flood It board and confirm that the only outlined tile is the Blue tile in the top-left corner.
- Make the first move with Coral. Click the Coral button below the board or press 2. The starting cell changes to Coral, and its connected Coral neighbors join your controlled region.
- Follow Route A in the table below. Make the remaining seven choices in this order: Blue, Gold, Teal, Coral, Blue, Gold, and Teal. With keyboard play, the complete sequence of key presses is 2, 1, 3, 4, 2, 1, 3, and 4, because keys 1 through 4 mean Blue, Coral, Gold, and Teal.
- Watch the move history as you play. For Route A, it should show C B G T C B G T. Each letter records one color selection.
- Confirm that the outline now covers all 25 tiles and that every tile shows the same color. The entire board, not merely the original corner area, must form one connected monochromatic region.
- If you made an unwanted selection, press Delete or Backspace before checking. Undo removes the latest color and deterministically replays the remaining history from the original board.
- While still on move eight, choose Check board or press Enter. A verified solved board awards exactly 1,000 points.
| Route | Internal ID sequence | Color-button sequence | Number-key sequence |
|---|---|---|---|
| A | 1, 0, 2, 3, 1, 0, 2, 3 | Coral, Blue, Gold, Teal, Coral, Blue, Gold, Teal | 2, 1, 3, 4, 2, 1, 3, 4 |
| B | 1, 3, 2, 1, 0, 2, 3, 1 | Coral, Teal, Gold, Coral, Blue, Gold, Teal, Coral | 2, 4, 3, 2, 1, 3, 4, 2 |
| C | 1, 3, 2, 3, 1, 0, 2, 3 | Coral, Teal, Gold, Teal, Coral, Blue, Gold, Teal | 2, 4, 3, 4, 2, 1, 3, 4 |
The internal IDs and keyboard numbers intentionally use different numbering. IDs run from 0 to 3 for Blue, Coral, Gold, and Teal, while the keyboard runs from 1 to 4 in that color order. Flood It accepts all three verified routes; it does not compare your play with one memorized answer. Avoid making a ninth move, because a monochromatic board earns 1,000 points only when checked at or before move eight.
Pointer and Keyboard Controls
The four large color buttons below the board provide the simplest pointer controls, while the keyboard can handle every part of a run.
| Task | Input | Result |
|---|---|---|
| Choose a color directly | Color buttons or keys 1-4 | Recolors the controlled region and absorbs matching orthogonal neighbors |
| Move the color cursor | Arrow keys | Cycles through the available color choices |
| Choose the selected color | Space | Makes the move represented by the current cursor |
| Undo a selection | Delete or Backspace | Removes the latest color and replays the remaining history |
| Check the result | Enter | Runs the board check against the completion and move-limit rules |
| Start over | Restart | Restores the same board with zero moves, zero mistakes, zero score, and Blue selected |
Repeated keydown events are ignored, so holding a key cannot consume several moves accidentally. Native buttons expose color names, current-color state, and keyboard selection to assistive technology. The bounded five-column board and 44-pixel color controls fit a 390-pixel viewport without horizontal scrolling, while the tile letters and controlled-region outline keep the puzzle readable without depending only on hue.
How Checks, Mistakes, and Scoring Work
Check board follows a clear three-part contract:
- Before move eight, an unsolved check is marked incomplete and adds no mistake.
- At eight or more moves, an unsolved check counts as a completed limit failure. The first failed limit check records one mistake but leaves the board and Undo active. A second failed limit check deadlocks the run until Restart.
- A monochromatic board checked at or before move eight is successful and earns exactly 1,000 points.
There is no speed bonus, move deduction, random modifier, or hidden partial credit. The 1,000-point result is the complete fixed value for solving this fixture within the proven limit. If you reach eight moves with an unsolved board, do not check again immediately: use Undo, remove one or more selections, and try a stronger sequence before creating the second failure.
Undo does not rely on a mutable snapshot. It removes the latest color from the visible history and deterministically replays every remaining selection from the original arrangement. This makes an incorrect branch repairable without changing the underlying board or the eight-move target.
Completion and deadlock are terminal states. Once either occurs, color choices, cursor movement, undo, and repeated checks no longer change the run. Restart is the clean way to begin again with the same fixed arrangement and a zeroed score.
Why Eight Moves Is the Proven Minimum
The general operation follows the rule described in Arthur, Clifford, Jalsenius, Montanaro, and Sach’s formal Flood-It complexity research, which defines a move as changing the monochromatic component connected to the top-left tile. Simon Tatham’s Flood documentation independently describes choosing a color to flood-fill the top-left region and completing the board within a move limit. These sources support the general game rule only; they do not define this particular fixture, palette, score, control scheme, or failure policy.
The fixture-specific proof is separate. A breadth-first search treats each complete board coloring as a state, tries the three colors different from the current top-left color, and visits each distinct board once. It finds 415 reachable boards, no solved board at depths zero through seven, and the first monochromatic board at depth eight. A second independent enumeration checks every legal eight-move color sequence and finds exactly the three routes shown above. The result establishes both sides of the claim: this board can be solved in eight moves, but it cannot be solved in fewer.
The disclosed row-major starting board is 01231 / 11320 / 20231 / 32102 / 13023, with 0 representing Blue, 1 Coral, 2 Gold, and 3 Teal. It never changes between sessions, and Restart restores the same arrangement, so the verification can be reproduced exactly rather than relying on an unrecorded random seed.
Browser Play and a Clean Finish
All rules and state transitions run locally in the browser. The game uploads no board history, requires no account, calls no remote game service, and requests no device permission. The visible score and locally stored best score belong to this local run rather than an online leaderboard.
After a successful check, the board should show one color across all 25 cells, the score should read 1,000, and the move history should contain eight selections. That result confirms completion of this one disclosed puzzle within its proven minimum limit; it does not measure intelligence, vision, attention, or educational ability. Restart and replay the fixed board whenever you want to practice a different verified route or compare how each early expansion changes your controlled territory.
For a deeper look, see Fraction Shape Puzzle for Beginners: Controls and Checks.