LeetCode 547 Number of Provinces - Input

LeetCode gives you isConnected, which is an adjacency matrix. isConnected[i][j] = 1 means there is an edge between cities $i$ and $j$. You need to convert this to DFS logic.

Instead of building an adjacency list, you can DFS directly on the matrix. When exploring neighbors of city $u$, loop through all cities $v$ from $0$ to $n-1$. If isConnected[u][v] = 1 and $v$ is not visited, recurse on $v$. This works fine for small $n$ (up to a few hundred). For large graphs, adjacency lists are faster.