public static void main(String[] args) {

int[] preorder = new int[]{7, 10, 4, 3, 1, 2, 8, 11};

int[] inorder = new int[]{4, 10, 3, 1, 7, 11, 8, 2};

// build b tree

Node bt = buildBTInorderPreorder(inorder, preorder);

bt.printBT();

}

public static HashMap<Integer, Integer> mapIndex(int[] inorder) {

HashMap<Integer, Integer> index = new HashMap<Integer, Integer>();

for (int i = 0; i < inorder.length; i++) {

index.put(inorder[i], i);

}

return index;

}

public static Node buildBTInorderPreorder(int[] in,

int[] pre) {

if (in.length == 0 || pre.length != in.length)

return null;

// get index of element of inOrder

HashMap<Integer, Integer> index = new HashMap<Integer, Integer>();

for (int i = 0; i < in.length; i++) {

index.put(in[i], i);

}

Node root = new Node(pre[0]);

int rootIndex = index.get(pre[0]);

root.left = buildBTInorderPreorder(Arrays.copyOfRange(in, 0, rootIndex),

Arrays.copyOfRange(pre, 1, rootIndex+1));

root.right = buildBTInorderPreorder(Arrays.copyOfRange(in, rootIndex + 1, in.length),

Arrays.copyOfRange(pre, rootIndex+1, pre.length));

return root;

}