Here is the interview question prompt, presented for reference.

Imagine the implementation for the paintbucket feature in Microsoft Paint, or how certain image filters work. You click on a specific pixel on a screen, and every similar-colored neighboring pixel would change to your selected color. Let's implement a simpler version of that feature.

You're given a n x n matrix array of numbers. Let's say you'd like to replace all similar and connected cells of a certain number with another, starting at column 0 and row 0.

So here's your input:

const input = [
  [1, 1, 1, 1, 1, 1, 1],
  [1, 1, 1, 1, 1, 1, 0],
  [1, 0, 0, 1, 1, 0, 1],
  [1, 2, 1, 2, 1, 2, 0],
  [1, 2, 1, 2, 2, 2, 0],
  [1, 2, 2, 2, 1, 2, 0],
  [1, 1, 1, 1, 1, 2, 1]
]

And the final result of starting at column 0 and row 0 would be as follows:

// floodFill(matrix, startingRow, startingCol, newValue)
floodFill(input, 0, 0, 3);
// [
//   [3, 3, 3, 3, 3, 3, 3],
//   [3, 3, 3, 3, 3, 3, 0],
//   [3, 0, 0, 3, 3, 0, 1],
//   [3, 2, 1, 2, 3, 2, 0],
//   [3, 2, 1, 2, 2, 2, 0],
//   [3, 2, 2, 2, 3, 2, 0],
//   [3, 3, 3, 3, 3, 2, 1]
// ]

Notice how all the 1s that were bordering the original 1 in column 0 and row 0 have been transformed to 3.

Constraints

• Given matrix contains non negative integers
• The array is 0-indexed
• Let |V|, |E| represent the number of vertices and edges of the graph (if you consider the matrix as a graph)
• Expected time complexity : O(|V|)
• Expected space complexity : O(|V|) considering the call stack

You can see the full challenge with visuals at this link.