CODE 27. Construct Binary Tree from Inorder and Postorder Traversal

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Given inorder and postorder traversal of a tree, construct the binary tree.
Note:
You may assume that duplicates do not exist in the tree.

public TreeNode buildTree(int[] inorder, int[] postorder) {
	// Start typing your Java solution below
	// DO NOT write main() function
	if (null == inorder || null == postorder || inorder.length <= 0
			|| postorder.length <= 0) {
		return null;
	}
	return dfs(inorder, postorder, 0, inorder.length - 1, 0,
			postorder.length - 1);
}

TreeNode dfs(int[] inorder, int[] postorder, int inorderStart,
		int inorderEnd, int postorderStart, int postorderEnd) {
	TreeNode node = new TreeNode(postorder[postorderEnd]);
	int nodeIndexInInorder = findElement(inorder, postorder[postorderEnd]);
	int leftLength = nodeIndexInInorder - inorderStart;
	int rightLength = inorderEnd - nodeIndexInInorder;
	if (leftLength > 0) {
		TreeNode left = dfs(inorder, postorder, inorderStart,
				nodeIndexInInorder - 1, postorderStart, postorderEnd
						- rightLength - 1);
		node.left = left;
	}
	if (rightLength > 0) {
		TreeNode right = dfs(inorder, postorder, nodeIndexInInorder + 1,
				inorderEnd, postorderEnd - rightLength, postorderEnd - 1);
		node.right = right;
	}
	return node;
}

int findElement(int[] array, int element) {
	for (int i = 0; i < array.length; i++) {
		if (array[i] == element) {
			return i;
		}
	}
	return -1;
}