427.建立四叉树

题解

题目：给一个数组，正方形的，如果其中某部分不是全1或全0，则分成4部分，变成四叉树

思路：递归，其实难点就在于分成四部分

TopLeft:     dfs(rowStart, (rowStart+rowEnd)/2, colStart, (colStart+colEnd)/2),
TopRight:    dfs(rowStart, (rowStart+rowEnd)/2, (colStart+colEnd)/2, colEnd),
BottomLeft:  dfs((rowStart+rowEnd)/2, rowEnd, colStart, (colStart+colEnd)/2),
BottomRight: dfs((rowStart+rowEnd)/2, rowEnd, (colStart+colEnd)/2, colEnd),

代码

type Node struct {
	Val         bool
	IsLeaf      bool
	TopLeft     *Node
	TopRight    *Node
	BottomLeft  *Node
	BottomRight *Node
}

func construct(grid [][]int) *Node {
	var dfs func(rowStart, rowEnd, colStart, colEnd int) *Node
	dfs = func(rowStart, rowEnd, colStart, colEnd int) *Node {
		for i := rowStart; i < rowEnd; i++ {
			for j := colStart; j < colEnd; j++ {
				if grid[i][j] != grid[rowStart][colStart] {
					return &Node{
						Val:         true,
						IsLeaf:      false,
						TopLeft:     dfs(rowStart, (rowStart+rowEnd)/2, colStart, (colStart+colEnd)/2),
						TopRight:    dfs(rowStart, (rowStart+rowEnd)/2, (colStart+colEnd)/2, colEnd),
						BottomLeft:  dfs((rowStart+rowEnd)/2, rowEnd, colStart, (colStart+colEnd)/2),
						BottomRight: dfs((rowStart+rowEnd)/2, rowEnd, (colStart+colEnd)/2, colEnd),
					}
				}
			}
		}
		return &Node{
			Val:         grid[rowStart][colStart] == 1,
			IsLeaf:      true,
			TopLeft:     nil,
			TopRight:    nil,
			BottomLeft:  nil,
			BottomRight: nil,
		}
	}
	return dfs(0, len(grid), 0, len(grid))
}