面试150 建立四叉树

思路

采用递归分治的思路构建四叉树。首先判断当前区域内的值是否全部相同，若是，则构建一个叶子节点；若否，则将区域划分为四个子区域（左上、右上、左下、右下），对每个子区域递归构建对应的子节点，并将其作为当前非叶子节点的四个子树。通过不断划分和合并，实现将二维网格压缩为一棵结构紧凑的四叉树。

"""
# Definition for a QuadTree node.
class Node:def __init__(self, val, isLeaf, topLeft, topRight, bottomLeft, bottomRight):self.val = valself.isLeaf = isLeafself.topLeft = topLeftself.topRight = topRightself.bottomLeft = bottomLeftself.bottomRight = bottomRight
"""class Solution:def construct(self, grid: List[List[int]]) -> 'Node':n=len(grid)def isSame(x,y,size):val=grid[x][y]for i in range(x,x+size):for j in range(y,y+size):if grid[i][j]!=val:return False,valreturn True,valdef build(x,y,size):same,val=isSame(x,y,size)if same:return Node(val==1,True)else:half=size//2return Node(val=True,isLeaf=False,topLeft=build(x,y,half),topRight=build(x,y+half,half),bottomLeft=build(x+half,y,half),bottomRight=build(x+half,y+half,half))return build(0,0,n)