```typescript
export function spanMerge(spans: number[][]): number[] {
  if (spans.length === 0) return [];

  const sorted = [...spans].sort((a, b) => a[0] - b[0]);

  const merged: number[] = [sorted[0]];

  for (let i = 1; i < sorted.length; i++) {
    const last = merged[merged.length - 1];
    const current = sorted[i];

    if (current[0] <= last[1]) {
      merged[merged.length - 1][1] = Math.max(last[1], current[1]);
    } else {
      merged.push(current);
    }
  }

  return merged;
}
```