Largest Number - Custom Comparator

You cannot sort by numeric value ($30 > 3$ but $"330" > "303"$). The key insight: compare two numbers $a$ and $b$ by checking if $ab > ba$ when concatenated as strings.

For $3$ and $30$: compare $"330"$ vs $"303"$. Since $"330" > "303"$, $3$ should come before $30$.

This comparison is transitive, so standard sorting algorithms work correctly with this custom comparator.