1 class Solution {
2 public TreeNode buildTree(int[] inorder, int[] postorder) {
3 return helper(postorder.length-1, 0, inorder.length - 1, inorder, postorder);
4
5 }
6
7 public TreeNode helper(int post, int inStart, int inEnd, int[] inorder, int[] postorder) {
8 if(inStart > inEnd || post < 0) {
9 return null;
10 }
11 TreeNode root = new TreeNode(postorder[post]);
12 int rootIndex = 0;
13 for(int i = inStart; i <= inEnd; i++) {
14 if(inorder[i] == root.val) {
15 rootIndex = i;
16 break;
17 }
18 }
19
20 root.right = helper(post-1, rootIndex+1, inEnd, inorder, postorder);
21 root.left = helper(post - (inEnd - rootIndex + 1), inStart, rootIndex - 1, inorder, postorder );
22 // inEnd - rootIndex注意是inEnd去减， 不是inorder.length
23 return root;
24 }
25 }
