Quiz: DP Details

Longest path DP in a DAG: dp[v] = 1 + max(dp[u]) for edges $u \to v$. What should dp[source] be initialized to?

1. A.$-\infty$ (we want maximum)
2. B.Undefined until computed
3. C.$1$ (source is one node)
4. D.$0$ (source contributes no edges yet)