2.重构二叉树

题目描述

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

代码

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


def reconstruct(pre,pre_start,pre_end,tin,tin_start,tin_end):
    if pre_start <= pre_end:
        root=TreeNode(pre[pre_start])
    else:
        root=None

    for i in range(tin_start,tin_end+1):
        if tin[i]==pre[pre_start]:
            length=i-tin_start
            root.left=reconstruct(pre,pre_start+1,pre_start+length,tin,tin_start,i-1)
            root.right=reconstruct(pre,pre_start+length+1,pre_end,tin,i+1,tin_end)
            break
        
    return root
      
pre=[1,2,4,7,3,5,6,8]
tin=[4,7,2,1,5,3,8,6]
root=reconstruct(pre,0,len(pre)-1,tin,0,len(tin)-1)
print(root.left)