LintCode（72）中序遍历和后序遍历树构造二叉树

题目

中序遍历和后序遍历树构造二叉树

分析

Python代码

"""
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
self.val = val
self.left, self.right = None, None
"""
def buildSubTree(inorder, inBeg, inEnd, postorder, postBeg, postEnd):
inLen = len(inorder)
postLen = len(postorder)
if inBeg == inEnd or inEnd > inLen or postBeg == postEnd or postEnd > postLen:
return None

root = TreeNode(postorder[postEnd - 1])
pos = inorder.index(root.val)

leftLen = pos - inBeg - 1
root.left = buildSubTree(inorder, inBeg, inBeg + leftLen + 1, postorder, postBeg, postBeg + leftLen + 1)
root.right = buildSubTree(inorder, inBeg + leftLen + 2, inEnd, postorder, postBeg + leftLen + 1, postEnd - 1)

return root

class Solution:
"""
@param inorder : A list of integers that inorder traversal of a tree
@param postorder : A list of integers that postorder traversal of a tree
@return : Root of a tree
"""

def buildTree(self, inorder, postorder):
# write your code here
return buildSubTree(inorder, 0, len(inorder), postorder, 0, len(postorder))

C++代码

/**
* Definition of TreeNode:
* class TreeNode {
* public:
*     int val;
*     TreeNode *left, *right;
*     TreeNode(int val) {
*         this->val = val;
*         this->left = this->right = NULL;
*     }
* }
*/

class Solution {
/**
*@param inorder : A list of integers that inorder traversal of a tree
*@param postorder : A list of integers that postorder traversal of a tree
*@return : Root of a tree
*/
public:
TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
// write your code here
return buildSubTree(inorder.begin(),inorder.end(),postorder.begin(),postorder.end());
}

TreeNode *buildSubTree(vector<int>::iterator inBeg, vector<int>::iterator inEnd,
vector<int>::iterator postBeg, vector<int>::iterator postEnd)
{
if(inBeg == inEnd || postBeg == postEnd)
{
return NULL;
}//if

TreeNode *root = new TreeNode(*(postEnd - 1));

vector<int>::iterator pos = find(inBeg, inEnd, root->val);

if(pos != inEnd)
{
int leftLen = pos - inBeg - 1;
root->left = buildSubTree(inBeg,inBeg+leftLen+1, postBeg,postBeg+leftLen+1);
root->right = buildSubTree(inBeg+leftLen+2,inEnd, postBeg+leftLen+1, postEnd -1 );
}//if

return root;
}
};