首页 > 代码库 > LeetCode: Construct Binary Tree from Preorder and Inorder Traversal 解题报告
LeetCode: Construct Binary Tree from Preorder and Inorder Traversal 解题报告
Construct Binary Tree from Preorder and Inorder Traversal
Given preorder and inorder traversal of a tree, construct the binary tree.
Note:
You may assume that duplicates do not exist in the tree.
SOLUTION 1:
1. Find the root node from the preorder.(it is the first node.)
2. Try to find the position of the root in the inorder. Then we can get the number of nodes in the left tree.
3. 递归调用，构造左子树和右子树。
例子：
Pre: 4 2 1 3 6 5 7
Inorder: 1 2 3 4 5 6 7
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */10 public class Solution {11 public TreeNode buildTree(int[] preorder, int[] inorder) {12 // bug 3: consider when length is 0.13 if (preorder == null || inorder == null || preorder.length == 0 || preorder.length != inorder.length) {14 return null;15 }16 17 // bug 4: end index is length - 1.18 return buildTree(preorder, inorder, 0, preorder.length - 1, 0, preorder.length - 1);19 }20 21 public TreeNode buildTree(int[] preorder, int[] inorder, int preStart, int preEnd, int inStart, int inEnd) {22 // base case;23 if (preStart > preEnd) {24 return null;25 }26 27 int rootVal = preorder[preStart];28 TreeNode root = new TreeNode(rootVal);29 30 int pos = findTarget(inorder, rootVal, inStart, inEnd);31 32 // bug 5: left number is pos - instart can‘t add 133 int leftNum = pos - inStart;34 35 root.left = buildTree(preorder, inorder, preStart + 1, preStart + leftNum, inStart, pos - 1);36 root.right = buildTree(preorder, inorder, preStart + leftNum + 1, preEnd, pos + 1, inEnd);37 38 return root;39 }40 41 // bug 1: return type required.42 // bug 2: this is not a bst. can‘t use binary search.43 public int findTarget(int[] A, int target, int start, int end) {44 for (int i = start; i <= end; i++) {45 if (target == A[i]) {46 return i;47 }48 }49 50 return -1;51 }52 }
GITHUB:
https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/tree/BuildTree.java
LeetCode: Construct Binary Tree from Preorder and Inorder Traversal 解题报告
声明：以上内容来自用户投稿及互联网公开渠道收集整理发布，本网站不拥有所有权，未作人工编辑处理，也不承担相关法律责任，若内容有误或涉及侵权可进行投诉： 投诉/举报 工作人员会在5个工作日内联系你，一经查实，本站将立刻删除涉嫌侵权内容。