LC733 Flood Fill

class Solution:
    def floodFill(self, image: List[List[int]], sr: int, sc: int, newColor: int) -> List[List[int]]:
        # time O(N) space O(1)
        # main idea: step1: check if start point has the same color the  recursion will never end; step2; dfs and set conditions to check 4 directions to avoid out of boundry # step3  return image 
        width = len(image[0])
        height = len(image)
        color = image[sr][sc]
        
        def _dfs(sr,sc):
            if 0 <= sr < height and 0 <= sc < width and image[sr][sc] == color :
                image[sr][sc] = newColor
                _dfs(sr+1,sc)
                _dfs(sr-1,sc)
                _dfs(sr,sc+1)
                _dfs(sr,sc-1)

        if color != newColor:
            _dfs(sr,sc)
            
        return image