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diff --git a/.gitignore b/.gitignore
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+++ b/.gitignore
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+/target
+tags
diff --git a/Cargo.lock b/Cargo.lock
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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "connect4"
+version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
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+++ b/Cargo.toml
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+[package]
+name = "connect4"
+version = "0.1.0"
+authors = ["Charles Cabergs <me@cacharle.xyz>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/README.md b/README.md
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+++ b/README.md
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+# connect4
+
+Connect 4 solver.
+
+## Resources
+
+* CodeBullet video - <https://www.youtube.com/watch?v=XRVA5PMSKKE>
+* Pascal Pons blog - <http://blog.gamesolver.org/>
diff --git a/src/main.rs b/src/main.rs
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+++ b/src/main.rs
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+const HEIGHT: u64 = 6;
+const WIDTH:  u64 = 7;
+
+type Bits = u64;
+
+/**
+ * bit order:
+ *
+ * .  .  .  .  .  .  .
+ * 5 12 19 26 33 40 47
+ * 4 11 18 25 32 39 46
+ * 3 10 17 24 31 38 45
+ * 2  9 16 23 30 37 44
+ * 1  8 15 22 29 36 43
+ * 0  7 14 21 28 35 42
+ *
+ * an extra row is added for the key represention
+ *
+ *
+ *
+ */
+struct Position {
+    /// stones of the current player
+    player: u64,
+    /// stones of the grid
+    mask:   u64,
+}
+
+impl Position {
+    fn new() -> Position {
+        Position{ player: 0, mask: 0 }
+    }
+
+    fn from_position(col_moves: &[u64]) -> Position {
+        let mut position = Position::new();
+        for col_pos in col_moves {
+            position.play(*col_pos);
+        }
+        position
+    }
+
+    fn play(&mut self, col_pos: u64) {
+        self.player ^= self.mask;
+        self.mask |= self.mask + (1 << (col_pos * (HEIGHT + 1)));
+    }
+
+    fn key(&self) -> u64 {
+        self.player + self.mask
+    }
+}
+
+use std::fmt;
+
+impl fmt::Debug for Position {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "mask: {:064b}\n", self.mask)?;
+        for i in 0..WIDTH {
+            write!(f, "\t{:07b}\n", (self.mask & (0b1111111 << (i * WIDTH))) >> (i * WIDTH));
+        }
+
+        write!(f, "player: {:064b}\n", self.player)?;
+        for i in 0..WIDTH {
+            write!(f, "\t{:07b}\n", (self.player & (0b1111111 << (i * WIDTH))) >> (i * WIDTH));
+        }
+
+        write!(f, "key: {:064b}\n", self.key())?;
+        for i in 0..WIDTH {
+            write!(f, "\t{:07b}\n", (self.key() & (0b1111111 << (i * WIDTH))) >> (i * WIDTH));
+        }
+        Ok(())
+    }
+}
+
+fn main() {
+    let mut p = Position::new();
+    // println!("{:?}", p);
+    p.play(2);
+    p.play(2);
+    p.play(1);
+    p.play(5);
+    p.play(5);
+    println!("{:?}", p);
+    // p.play(4);
+    // println!("------------------------------");
+    // println!("{:?}", p);
+}