标签：__init__ object start size ret lis dtree for restart
Given preorder and inorder traversal of a tree, construct the binary tree.
Note:
You may assume that duplicates do not exist in the tree.
For example, given
preorder = [3,9,20,15,7] inorder = [9,3,15,20,7]
Return the following binary tree:
3
/ 9 20
/ 15 7
Approach #1: C++.
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
return solve(preorder, 0, inorder, 0, inorder.size()-1);
}
private:
TreeNode* solve(vector<int>& preorder, int ps, vector<int>& inorder, int is, int ie) {
if (ps > preorder.size() || is > ie) return NULL;
TreeNode* root = new TreeNode(preorder[ps]);
int inIndex = 0;
for (int i = is; i <= ie; ++i)
if (inorder[i] == root->val)
inIndex = i;
TreeNode* leftchild = solve(preorder, ps+1, inorder, is, inIndex-1);
TreeNode* rightchild = solve(preorder, ps+inIndex-is+1, inorder, inIndex+1, ie);
root->left = leftchild;
root->right = rightchild;
return root;
}
};
Approach #2: Java.
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode buildTree(int[] preorder, int[] inorder) {
return helper(0, 0, inorder.length - 1, preorder, inorder);
}
private TreeNode helper(int preStart, int inStart, int inEnd, int[] preorder, int[] inorder) {
if (preStart > preorder.length - 1 || inStart > inEnd) return null;
TreeNode root = new TreeNode(preorder[preStart]);
int inIndex = 0;
for (int i = inStart; i <= inEnd; ++i) {
if (inorder[i] == root.val)
inIndex = i;
}
root.left = helper(preStart + 1, inStart, inIndex - 1, preorder, inorder);
root.right = helper(preStart + inIndex - inStart + 1, inIndex + 1, inEnd, preorder, inorder);
return root;
}
}
Approach #3: Python.
# 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 buildTree(self, preorder, inorder):
"""
:type preorder: List[int]
:type inorder: List[int]
:rtype: TreeNode
"""
if inorder:
ind = inorder.index(preorder.pop(0))
root = TreeNode(inorder[ind])
root.left = self.buildTree(preorder, inorder[0:ind])
root.right = self.buildTree(preorder, inorder[ind+1:])
return root
Construct Binary Tree from Preorder and Inorder Traversal
标签：__init__ object start size ret lis dtree for restart
原文地址：https://www.cnblogs.com/ruruozhenhao/p/10003292.html
