import { z } from "npm:zod"; export const COLS = 7; export const ROWS = 6; export type Winner = { kind: "winner"; winner: number; }; export type Draw = { kind: "draw"; }; export type Result = Winner | Draw; export type InProgress = { status: "in_progress"; next_player: number; }; export type Over = { status: "over"; result: Result; }; export type Status = InProgress | Over; const stringOrNumber = z.union([z.string(), z.number()]); export const PlayerI = z.number().nonnegative().lte(1); export const Slot = z.nullable(PlayerI); export type Slot = z.infer; export const Column = z.array(Slot).length(6); export type Column = z.infer; export const Board = z.array(Column).length(7); export type Board = z.infer; export const State = z.object({ next_player: PlayerI, board: Board, }); export type State = z.infer; export const Action = z.object({ player: z.coerce.number().nonnegative().lte(1), column: z.coerce.number().nonnegative().lt(COLS), }); export type Action = z.infer; export function get(state: State, col: number, row: number): Slot { return state.board[col][row]; } export function set(state: State, col: number, row: number, slot: Slot): void { state.board[col][row] = slot; } export type ActionCheck = | "ok" | "wrong_player" | "column_full" | "column_out_of_bounds"; export function check_action(state: State, action: Action): ActionCheck { if (action.player !== state.next_player) { return "wrong_player"; } if (action.column < 0 || action.column >= COLS) { return "column_out_of_bounds"; } if (get(state, action.column, ROWS - 1) !== null) { return "column_full"; } return "ok"; } function check_slots_eq(a: Slot, b: Slot, c: Slot, d: Slot): Slot { if (a === b && b === c && c === d) { return a; } return null; } export function status(state: State): Status { // Check Vertical Win for (let col = 0; col < COLS; col++) { for (let row = 0; row < 3; row++) { let check = check_slots_eq( get(state, col, row + 0), get(state, col, row + 1), get(state, col, row + 2), get(state, col, row + 3) ); if (check !== null) { return { status: "over", result: { kind: "winner", winner: check } }; } } } // Check Horizontal Win for (let row = 0; row < ROWS; row++) { for (let col = 0; col < 4; col++) { let check = check_slots_eq( get(state, col + 0, row), get(state, col + 1, row), get(state, col + 2, row), get(state, col + 3, row) ); if (check !== null) { return { status: "over", result: { kind: "winner", winner: check } }; } } } // Check Diagonal Up Win for (let col = 0; col < 4; col++) { for (let row = 0; row < 3; row++) { let check = check_slots_eq( get(state, col + 0, row + 0), get(state, col + 1, row + 1), get(state, col + 2, row + 2), get(state, col + 3, row + 3) ); if (check !== null) { return { status: "over", result: { kind: "winner", winner: check } }; } } } // Check Diagonal Down Win for (let col = 0; col < 4; col++) { for (let row = 3; row < 6; row++) { let check = check_slots_eq( get(state, col + 0, row - 0), get(state, col + 1, row - 1), get(state, col + 2, row - 2), get(state, col + 3, row - 3) ); if (check !== null) { return { status: "over", result: { kind: "winner", winner: check } }; } } } // Check For Possible Moves for (let col = 0; col < COLS; col++) { if (get(state, col, ROWS - 1) === null) { return { status: "in_progress", next_player: state.next_player }; } } // No Possible Moves, Draw return { status: "over", result: { kind: "draw" } }; } export function apply_action(state: State, action: Action): Status { // Action should be checked before calling this function. // We assert that the action is ok. let check = check_action(state, action); switch (check) { case "wrong_player": throw new Error(`It is not player ${action.player}'s turn`); case "column_full": throw new Error(`Column ${action.column} is full`); case "column_out_of_bounds": throw new Error(`Column ${action.column} is out of bounds`); case "ok": for (let row = 0; row < ROWS; row++) { if (get(state, action.column, row) === null) { set(state, action.column, row, action.player); state.next_player = 1 - action.player; return status(state); } } throw new Error("unreachable"); } }

connect4_random_agent