Log the number of dancing link updates

src/sudoku/math.ts

@@ -141,7 +141,7 @@ export class SudokuMath {
     return [...firstRow, ...Array(this.values2 - this.values).fill(0)];
   }
 
-  generateComplete() {
+  generateComplete(): [number[], number] {
     const result = this._baseBoard();
     const [header] = this.getDLXHeader(result, true);
 
@@ -157,16 +157,15 @@ export class SudokuMath {
     const dlx = new DLX(header, callback);
 
     dlx.search();
-    return result;
+    return [result, dlx.updates];
   }
 
   generate(clues: number, attempts = Infinity, totalTime = Infinity) {
-    const completed = this.generateComplete();
+    const [completed, updates] = this.generateComplete();
 
     const [header, dlxRows] = this.getDLXHeader(); // complete header - no candidates removed
 
     let solutions = 0;
-    let updates = 0;
     const dlx = new DLX(header, () => ++solutions >= 2);
 
     const candidates: DNode[][] = Array.from(Array(this.values2), () =>