```ts
export function mergeIntervals(intervals: number[][]): number[][] {
  if (intervals.length === 0) return [];
  
  const sortedIntervals = intervals.sort((a, b) => a[0] - b[0]);
  const merged: number[][] = [sortedIntervals[0]];
  
  for (let i = 1; i < sortedIntervals.length; i++) {
    const lastMerged = merged[merged.length - 1];
    const current = sortedIntervals[i];
    
    if (current[0] <= lastMerged[1]) {
      merged[merged.length - 1] = [lastMerged[0], Math.max(lastMerged[1], current[1])];
    } else {
      merged.push(current);
    }
  }
  
  return merged;
}
```