diff --git a/src/lib/board.spec.ts b/src/lib/board.spec.ts
index 1406ffa..6084b3d 100644
--- a/src/lib/board.spec.ts
+++ b/src/lib/board.spec.ts
@@ -10,12 +10,19 @@ void t.test("Serialize / deserialize", async (t) => {
     return board;
   };
 
-  void t.test("0x0 board", async (t) => {
+  void t.test("1x0 board", async (t) => {
     const board = createAndCheckBoard(t, "");
     t.throws(() => board.get(0, 0), { message: "Out of bounds: 0:0" });
     t.throws(() => board.get(0, 1), { message: "Out of bounds: 0:1" });
     t.throws(() => board.get(1, 0), { message: "Out of bounds: 1:0" });
     t.throws(() => board.get(1, 1), { message: "Out of bounds: 1:1" });
+
+    t.equal(board.hasRow(0), true);
+    t.equal(board.hasRow(1), false);
+    t.equal(board.hasSquare(0, 0), false);
+    t.equal(board.hasSquare(0, 1), false);
+    t.equal(board.hasSquare(1, 0), false);
+    t.equal(board.hasSquare(1, 1), false);
   });
 
   void t.test("Empty 1x1 board", async (t) => {
@@ -24,6 +31,13 @@ void t.test("Serialize / deserialize", async (t) => {
     t.throws(() => board.get(0, 1), { message: "Out of bounds: 0:1" });
     t.throws(() => board.get(1, 0), { message: "Out of bounds: 1:0" });
     t.throws(() => board.get(1, 1), { message: "Out of bounds: 1:1" });
+
+    t.equal(board.hasRow(0), true);
+    t.equal(board.hasRow(1), false);
+    t.equal(board.hasSquare(0, 0), true);
+    t.equal(board.hasSquare(0, 1), false);
+    t.equal(board.hasSquare(1, 0), false);
+    t.equal(board.hasSquare(1, 1), false);
   });
 
   void t.test("1x1 board with X", async (t) => {
@@ -32,6 +46,13 @@ void t.test("Serialize / deserialize", async (t) => {
     t.throws(() => board.get(0, 1), { message: "Out of bounds: 0:1" });
     t.throws(() => board.get(1, 0), { message: "Out of bounds: 1:0" });
     t.throws(() => board.get(1, 1), { message: "Out of bounds: 1:1" });
+
+    t.equal(board.hasRow(0), true);
+    t.equal(board.hasRow(1), false);
+    t.equal(board.hasSquare(0, 0), true);
+    t.equal(board.hasSquare(0, 1), false);
+    t.equal(board.hasSquare(1, 0), false);
+    t.equal(board.hasSquare(1, 1), false);
   });
 
   void t.test("Half-full 3x4 board", async (t) => {
@@ -56,6 +77,12 @@ void t.test("Serialize / deserialize", async (t) => {
     t.throws(() => board.get(4, 1), { message: "Out of bounds: 4:1" });
     t.throws(() => board.get(4, 2), { message: "Out of bounds: 4:2" });
     t.throws(() => board.get(4, 3), { message: "Out of bounds: 4:3" });
+
+    t.equal(board.hasRow(3), true);
+    t.equal(board.hasRow(4), false);
+    t.equal(board.hasSquare(3, 2), true);
+    t.equal(board.hasSquare(3, 3), false);
+    t.equal(board.hasSquare(4, 0), false);
   });
 
   void t.test("Validation", async (t) => {
diff --git a/src/lib/board.ts b/src/lib/board.ts
index 155e61f..da17a9c 100644
--- a/src/lib/board.ts
+++ b/src/lib/board.ts
@@ -4,6 +4,14 @@ import { unreachable } from "./utils.ts";
 export class Board {
   constructor(private readonly state: SquareState[][]) {}
 
+  hasRow(row: number) {
+    return !!this.state[row];
+  }
+
+  hasSquare(row: number, column: number) {
+    return !!this.state[row]?.[column];
+  }
+
   get(row: number, column: number) {
     const result = this.state[row]?.[column];
     if (!result) {
diff --git a/src/lib/solver.spec.ts b/src/lib/solver.spec.ts
new file mode 100644
index 0000000..853e46a
--- /dev/null
+++ b/src/lib/solver.spec.ts
@@ -0,0 +1,282 @@
+import t from "tap";
+
+import { getBoardOutcome, getSequenceOutcome } from "./solver.ts";
+import { CurrentOutcome, SquareState } from "./types.ts";
+import { Board } from "./board.ts";
+
+void t.test("getSequenceOutcome", async (t) => {
+  void t.test("empty sequence", async (t) => {
+    t.equal(getSequenceOutcome([]), null);
+  });
+
+  void t.test("all sequences of length 1", async (t) => {
+    t.equal(getSequenceOutcome([SquareState.Unoccupied]), null);
+    t.equal(getSequenceOutcome([SquareState.X]), CurrentOutcome.WinX);
+    t.equal(getSequenceOutcome([SquareState.O]), CurrentOutcome.WinO);
+  });
+
+  void t.test("all sequences of length 2", async (t) => {
+    t.equal(
+      getSequenceOutcome([SquareState.Unoccupied, SquareState.Unoccupied]),
+      null,
+    );
+    t.equal(getSequenceOutcome([SquareState.Unoccupied, SquareState.X]), null);
+    t.equal(getSequenceOutcome([SquareState.Unoccupied, SquareState.O]), null);
+    t.equal(getSequenceOutcome([SquareState.X, SquareState.Unoccupied]), null);
+    t.equal(
+      getSequenceOutcome([SquareState.X, SquareState.X]),
+      CurrentOutcome.WinX,
+    );
+    t.equal(getSequenceOutcome([SquareState.X, SquareState.O]), null);
+    t.equal(getSequenceOutcome([SquareState.O, SquareState.Unoccupied]), null);
+    t.equal(getSequenceOutcome([SquareState.O, SquareState.X]), null);
+    t.equal(
+      getSequenceOutcome([SquareState.O, SquareState.O]),
+      CurrentOutcome.WinO,
+    );
+  });
+
+  void t.test("sequences of length 7", async (t) => {
+    void t.test("all X except for the first element", async (t) => {
+      t.equal(
+        getSequenceOutcome([
+          SquareState.Unoccupied,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+        ]),
+        null,
+      );
+      t.equal(
+        getSequenceOutcome([
+          SquareState.O,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+        ]),
+        null,
+      );
+    });
+
+    void t.test("all X except for the last element", async (t) => {
+      t.equal(
+        getSequenceOutcome([
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.Unoccupied,
+        ]),
+        null,
+      );
+      t.equal(
+        getSequenceOutcome([
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.O,
+        ]),
+        null,
+      );
+    });
+
+    void t.test("all X except for the middle element", async (t) => {
+      t.equal(
+        getSequenceOutcome([
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.Unoccupied,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+        ]),
+        null,
+      );
+      t.equal(
+        getSequenceOutcome([
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+          SquareState.O,
+          SquareState.X,
+          SquareState.X,
+          SquareState.X,
+        ]),
+        null,
+      );
+    });
+
+    t.equal(
+      getSequenceOutcome([
+        SquareState.X,
+        SquareState.X,
+        SquareState.X,
+        SquareState.X,
+        SquareState.X,
+        SquareState.X,
+        SquareState.X,
+      ]),
+      CurrentOutcome.WinX,
+    );
+  });
+});
+
+void t.test("getBoardOutcome", async (t) => {
+  void t.test("2x2 boards", async (t) => {
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("__|__")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XX|X_")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XX|XX")),
+      CurrentOutcome.Draw,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("OO|OO")),
+      CurrentOutcome.Draw,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XO|OX")),
+      CurrentOutcome.Draw,
+    );
+  });
+
+  void t.test("3x3 boards", async (t) => {
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("___|___|___")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("___|_X_|___")),
+      CurrentOutcome.Undecided,
+    );
+
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XX_|___|___")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("___|___|_XX")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("X__|X__|___")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("___|__X|__X")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("X__|_X_|___")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("___|_X_|__X")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("__X|_X_|___")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("___|_X_|X__")),
+      CurrentOutcome.Undecided,
+    );
+
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XXX|O_O|O_O")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("O_O|O_O|XXX")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XOO|X__|XOO")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("OOX|__X|OOX")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XOO|OXO|OOX")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("OOX|OXO|XOO")),
+      CurrentOutcome.WinX,
+    );
+
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XXO|XOX|OXX")),
+      CurrentOutcome.WinO,
+    );
+
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XOX|XXO|OXO")),
+      CurrentOutcome.Draw,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XOX|XXO|OX_")),
+      CurrentOutcome.Undecided,
+    );
+  });
+
+  void t.test("5x5 boards", async (t) => {
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("_____|_____|_____|_____|_____")),
+      CurrentOutcome.Undecided,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("XXX__|_____|_____|_____|_____")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("X____|X____|X____|_____|_____")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("X____|_X___|__X__|_____|_____")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("__X__|_X___|X____|_____|_____")),
+      CurrentOutcome.WinX,
+    );
+
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("_____|_____|_____|_____|__XXX")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("_____|_____|____X|____X|____X")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("_____|_____|__X__|___X_|____X")),
+      CurrentOutcome.WinX,
+    );
+    t.equal(
+      getBoardOutcome(Board.fromSerialized("_____|_____|____X|___X_|__X__")),
+      CurrentOutcome.WinX,
+    );
+  });
+});
diff --git a/src/lib/solver.ts b/src/lib/solver.ts
new file mode 100644
index 0000000..f5e3c47
--- /dev/null
+++ b/src/lib/solver.ts
@@ -0,0 +1,90 @@
+import { Board } from "./board.ts";
+import { CurrentOutcome, SquareState } from "./types.ts";
+
+export const getSequenceOutcome = (sequence: SquareState[]) => {
+  for (let i = 1; i < sequence.length; i++) {
+    if (sequence[i - 1] != sequence[i]) {
+      return null;
+    }
+  }
+
+  switch (sequence[0]) {
+    case SquareState.X:
+      return CurrentOutcome.WinX;
+    case SquareState.O:
+      return CurrentOutcome.WinO;
+    default:
+      return null;
+  }
+};
+
+export const getBoardOutcome = (board: Board) => {
+  for (let row = 0; board.hasRow(row); row++) {
+    for (let column = 2; board.hasSquare(row, column); column++) {
+      const tripleLeft = [
+        board.get(row, column - 2),
+        board.get(row, column - 1),
+        board.get(row, column - 0),
+      ];
+
+      const outcome = getSequenceOutcome(tripleLeft);
+      if (outcome) {
+        return outcome;
+      }
+    }
+  }
+
+  for (let row = 2; board.hasRow(row); row++) {
+    for (let column = 0; board.hasSquare(row, column); column++) {
+      const tripleUp = [
+        board.get(row - 2, column),
+        board.get(row - 1, column),
+        board.get(row - 0, column),
+      ];
+
+      const outcome = getSequenceOutcome(tripleUp);
+      if (outcome) {
+        return outcome;
+      }
+    }
+  }
+
+  for (let row = 2; board.hasRow(row); row++) {
+    for (let column = 2; board.hasSquare(row, column); column++) {
+      {
+        const tripleUpLeft = [
+          board.get(row - 2, column - 2),
+          board.get(row - 1, column - 1),
+          board.get(row - 0, column - 0),
+        ];
+        const upLeftOutcome = getSequenceOutcome(tripleUpLeft);
+        if (upLeftOutcome) {
+          return upLeftOutcome;
+        }
+      }
+
+      {
+        const tripleCross = [
+          board.get(row - 0, column - 2),
+          board.get(row - 1, column - 1),
+          board.get(row - 2, column - 0),
+        ];
+
+        const crossOutcome = getSequenceOutcome(tripleCross);
+        if (crossOutcome) {
+          return crossOutcome;
+        }
+      }
+    }
+  }
+
+  for (let row = 0; board.hasRow(row); row++) {
+    for (let column = 0; board.hasSquare(row, column); column++) {
+      if (board.get(row, column) === SquareState.Unoccupied) {
+        return CurrentOutcome.Undecided;
+      }
+    }
+  }
+
+  return CurrentOutcome.Draw;
+};
diff --git a/src/lib/types.ts b/src/lib/types.ts
index 048c923..a4f63bd 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -3,3 +3,10 @@ export enum SquareState {
   X,
   O,
 }
+
+export enum CurrentOutcome {
+  Undecided = 1,
+  Draw,
+  WinX,
+  WinO,
+}