Leetcode 655. Print Binary Tree 打印二叉树 解题报告

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给一个二叉树，要求进行打印，也就是在一个高度*宽度的矩阵里面打印就好了，每个子树的root打印在当前子区间的中间就好了

Print a binary tree in an m*n 2D string array following these rules:

The row number m should be equal to the height of the given binary tree.
The column number n should always be an odd number.
The root node's value (in string format) should be put in the exactly middle of the first row it can be put. The column and the row where the root node belongs will separate the rest space into two parts (left-bottom part and right-bottom part). You should print the left subtree in the left-bottom part and print the right subtree in the right-bottom part. The left-bottom part and the right-bottom part should have the same size. Even if one subtree is none while the other is not, you don't need to print anything for the none subtree but still need to leave the space as large as that for the other subtree. However, if two subtrees are none, then you don't need to leave space for both of them.
Each unused space should contain an empty string "".
Print the subtrees following the same rules.
Example 1:
Input:
     1
    /
   2
Output:
[["", "1", ""],
 ["2", "", ""]]
Example 2:
Input:
     1
    / \
   2   3
    \
     4
Output:
[["", "", "", "1", "", "", ""],
 ["", "2", "", "", "", "3", ""],
 ["", "", "4", "", "", "", ""]]
Example 3:
Input:
      1
     / \
    2   5
   / 
  3 
 / 
4 
Output:

[["",  "",  "", "",  "", "", "", "1", "",  "",  "",  "",  "", "", ""]
 ["",  "",  "", "2", "", "", "", "",  "",  "",  "",  "5", "", "", ""]
 ["",  "3", "", "",  "", "", "", "",  "",  "",  "",  "",  "", "", ""]
 ["4", "",  "", "",  "", "", "", "",  "",  "",  "",  "",  "", "", ""]]
Note: The height of binary tree is in the range of [1, 10].

总的来说就是，第一次dfs获得树的高度，第二次打印，注意根据当前层高计算相应的移动位置就可以了

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def printTree(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[str]]
        """
        import math
        def dfs(root, h):
            if root:
                return max(dfs(root.left,h+1), dfs(root.right,h+1))
            else :
                return h
        height = dfs(root, 0)
        width = 2 ** height -1
        # 初始化
        res = [ ["" for j in range(width)] for i in range(height)]
        # dfs print
        def dfs_print(res,root,h,pos):
            if root:
                res[h - 1][pos] = '%d' % root.val
                dfs_print(res, root.left, h+1, pos-2**(height - h - 1))
                dfs_print(res, root.right, h+1, pos+2**(height - h - 1))
        dfs_print(res,root,1,width/2)
        return res