106. Construct Binary Tree from Inorder and Postorder Traversal
Given two integer arrays inorder and postorder where inorder is the inorder traversal of a binary tree and postorder is the postorder traversal of the same tree, construct and return the binary tree.
Example 1:
Input: inorder = [9,3,15,20,7], postorder = [9,15,7,20,3]
Output: [3,9,20,null,null,15,7]
Example 2:
Input: inorder = [-1], postorder = [-1]
Output: [-1]
Constraints:
- 1 <= inorder.length <= 3000
- postorder.length == inorder.length
- -3000 <= inorder[i], postorder[i] <= 3000
- inorder and postorder consist of unique values.
- Each value of postorder also appears in inorder.
- inorder is guaranteed to be the inorder traversal of the tree.
- postorder is guaranteed to be the postorder traversal of the tree.
/**
* 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[] inorder, int[] postorder) {
if(inorder==null||postorder==null||inorder.length==0||postorder.length==0){
return null;
}
TreeNode treeNode = new TreeNode(postorder[postorder.length-1]);
for(int i=0;i<inorder.length;i++){
if(inorder[i]==postorder[postorder.length-1]){
treeNode.left = buildTree(Arrays.copyOfRange(inorder, 0, i),
Arrays.copyOfRange(postorder, 0, i));
treeNode.right = buildTree(Arrays.copyOfRange(inorder, i+1, inorder.length),
Arrays.copyOfRange(postorder, i, postorder.length-1));
}
}
return treeNode;
}
}