starting new structure

src_old/sudoku/validate-board.ts

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+/**
+ * Validate a fully filled Sudoku board (81-char string)
+ * Returns true if:
+ *  - 81 characters long
+ *  - all characters are digits 1–9
+ *  - all rows, columns, and 3×3 boxes sum to 45
+ */
+export function validateFullBoard(board: string): boolean {
+  // --- Basic sanity ---
+  if (board.length !== 81) return false;
+  if (!/^[1-9]+$/.test(board)) return false;
+
+  const getCell = (r: number, c: number) => Number(board[r * 9 + c]);
+
+  // --- Validate rows ---
+  for (let r = 0; r < 9; r++) {
+    const sum = Array.from({ length: 9 }, (_, c) => getCell(r, c))
+      .reduce((a, b) => a + b, 0);
+    if (sum !== 45) return false;
+  }
+
+  // --- Validate columns ---
+  for (let c = 0; c < 9; c++) {
+    const sum = Array.from({ length: 9 }, (_, r) => getCell(r, c))
+      .reduce((a, b) => a + b, 0);
+    if (sum !== 45) return false;
+  }
+
+  // --- Validate 3×3 boxes ---
+  for (let br = 0; br < 3; br++) {
+    for (let bc = 0; bc < 3; bc++) {
+      const sum = Array.from({ length: 9 }, (_, i) => {
+        const r = br * 3 + Math.floor(i / 3);
+        const c = bc * 3 + (i % 3);
+        return getCell(r, c);
+      }).reduce((a, b) => a + b, 0);
+      if (sum !== 45) return false;
+    }
+  }
+
+  return true;
+}
+/**
+ * 🔍 Assert that a Sudoku board string represents a valid, fully filled grid.
+ *
+ * Format:
+ *  - 81 characters
+ *  - Only digits 1–9
+ *  - Each row, column, and 3×3 box contains unique digits that sum to 45
+ *
+ * Throws descriptive errors on failure.
+ */
+
+export function assertValidFullBoard(board: string): void {
+  // --- Basic integrity checks ---
+  console.assert(board.length === 81, `❌ Board length must be 81, got ${board.length}`);
+  if (board.length !== 81) throw new Error(`Invalid board length: ${board.length}`);
+
+  // All characters must be digits 1–9
+  console.assert(/^[1-9]+$/.test(board), "❌ Board must contain only digits 1–9 (no 0s or dots)");
+  if (!/^[1-9]+$/.test(board)) throw new Error("Board contains invalid characters");
+
+  const get = (r: number, c: number) => Number(board[r * 9 + c]);
+
+  // --- Helper to assert uniqueness and sum ---
+  const assertGroup = (label: string, cells: number[]) => {
+    const sum = cells.reduce((a, b) => a + b, 0);
+    const unique = new Set(cells);
+    console.assert(sum === 45, `❌ ${label} sum=${sum} (should be 45)`);
+    console.assert(unique.size === 9, `❌ ${label} has duplicates: [${cells.join(",")}]`);
+
+    if (sum !== 45) throw new Error(`${label} does not sum to 45`);
+    if (unique.size !== 9) throw new Error(`${label} contains duplicates`);
+  };
+
+  // --- Validate rows ---
+  for (let r = 0; r < 9; r++) {
+    const row = Array.from({ length: 9 }, (_, c) => get(r, c));
+    assertGroup(`Row ${r + 1}`, row);
+  }
+
+  // --- Validate columns ---
+  for (let c = 0; c < 9; c++) {
+    const col = Array.from({ length: 9 }, (_, r) => get(r, c));
+    assertGroup(`Column ${c + 1}`, col);
+  }
+
+  // --- Validate 3×3 boxes ---
+  for (let br = 0; br < 3; br++) {
+    for (let bc = 0; bc < 3; bc++) {
+      const box: number[] = [];
+      for (let r = 0; r < 3; r++) {
+        for (let c = 0; c < 3; c++) {
+          box.push(get(br * 3 + r, bc * 3 + c));
+        }
+      }
+      const idx = br * 3 + bc + 1;
+      assertGroup(`Box ${idx}`, box);
+    }
+  }
+}
+
+
+