E-733. Flood Fill

# 起始颜色不和新色相同，并且
# 相邻颜色和旧色相同
# 并且都在有效范围内，则染色。
# O(N), O(N)
class Solution:    
    def floodFill(self, image: List[List[int]], sr: int, sc: int, newColor: int) -> List[List[int]]:
        def change_color(sr, sc):
            if image[sr][sc] == old_color:
                image[sr][sc] = newColor
                if sr > 0: 
                    change_color(sr - 1, sc)
                if sr < max_row:
                    change_color(sr + 1, sc)
                if sc < max_col:
                    change_color(sr, sc + 1)
                if sc > 0:
                    change_color(sr, sc - 1)
        old_color = image[sr][sc]
        max_row = len(image)-1
        max_col = len(image[0]) - 1
        if sr >= 0 and sr <= max_row and sc >= 0 and sc <= max_col and image[sr][sc] != newColor :
            change_color(sr, sc)
        return image