标签：bsp int rsa order and public binary iter topic
题目：
Given preorder and inorder traversal of a tree, construct the binary tree.
Note:
You may assume that duplicates do not exist in the tree.
链接： http://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/
6/7/2017
抄别人的答案
21ms, 29%
注意的地方
1. 题目中给出了节点没有重复值，所以可以利用第17行开始的循环
2. 第4行和第10行应该用exception，但是目前并不熟悉
3. 注意第24，25行的各个下标，preorder时候左子树最后一个节点的下一个就是右子树第一个节点，而inorder时候中间还隔着一个root节点
1 public class Solution { 2 public TreeNode buildTree(int[] preorder, int[] inorder) { 3 if (preorder == null || inorder == null) { 4 return null; 5 } 6 return buildTree(preorder, 0, preorder.length - 1, inorder, 0, inorder.length - 1); 7 } 8 private TreeNode buildTree(int[] preorder, int preLo, int preHi, int[] inorder, int inLo, int inHi) { 9 if (preorder == null || inorder == null) { 10 return null; 11 } 12 if (preLo > preHi || inLo > inHi) { 13 return null; 14 } 15 TreeNode node = new TreeNode(preorder[preLo]); 16 int rootInorderIndex = inLo; 17 for (int i = inLo; i <= inHi; i++) { 18 if (inorder[i] == node.val) { // no duplicate 19 rootInorderIndex = i; 20 break; 21 } 22 } 23 int leftTreeLength = rootInorderIndex - inLo; 24 node.left = buildTree(preorder, preLo + 1, preLo + leftTreeLength, inorder, inLo, rootInorderIndex - 1); 25 node.right = buildTree(preorder, preLo + 1 + leftTreeLength, preHi, inorder, rootInorderIndex + 1, inHi); 26 return node; 27 } 28 }
别人的做法：
iterative:尚未看懂
https://discuss.leetcode.com/topic/795/the-iterative-solution-is-easier-than-you-think
另一个没看懂的答案
https://discuss.leetcode.com/topic/16221/simple-o-n-without-map
1 def buildTree(self, preorder, inorder): 2 def build(stop): 3 if inorder and inorder[-1] != stop: 4 root = TreeNode(preorder.pop()) 5 root.left = build(root.val) 6 inorder.pop() 7 root.right = build(stop) 8 return root 9 preorder.reverse() 10 inorder.reverse() 11 return build(None)
更多讨论
https://discuss.leetcode.com/category/113/construct-binary-tree-from-preorder-and-inorder-traversal
105. Construct Binary Tree from Preorder and Inorder Traversal
标签：bsp int rsa order and public binary iter topic
原文地址：http://www.cnblogs.com/panini/p/6958817.html
