題目

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

方法

依據樹的中序遍歷和後序遍歷，來恢復樹，使用遞歸的思想。

	TreeNode getTree(int[] inorder, int inStart, int inEnd, int[] postorder, int postStart, int postEnd) {
		if (inStart >= inEnd) {
			return null;
		}
		int cur = postorder[postEnd - 1];
		TreeNode root = new TreeNode(cur);
		int i = 0;
		int j = inStart;
		while(inorder[j] != cur) {
			j++;
			i++;
		}
		
		
		root.left = getTree(inorder, inStart, inStart + i, postorder, postStart, postStart + i);
		root.right = getTree(inorder, inStart + i + 1, inEnd, postorder, postStart + i, postEnd - 1);
		
		return root;
	}
    public TreeNode buildTree(int[] inorder, int[] postorder) {
    	if (inorder == null) {
    		return null;
    	}
    	int len = inorder.length;
    	return getTree(inorder, 0, len, postorder, 0, len);
    }

Construct Binary Tree from Inorder and Postorder Traversal