public class BinaryTreeInorderPreorder {

public TreeNode buildTree(int[] preorder, int[] inorder) {

int len_pre = preorder.length;

int len_in = inorder.length;

if (len_pre == 0 || len_in == 0 || len_pre != len_in) {

return null;

}

return recur(preorder, inorder, 0, len_in - 1, 0, len_pre - 1);

}

public TreeNode recur(int[] pre, int[] in, int instart, int inend, int prestart, int preend) {

System.out.println("instart = " + instart + "; inend = " + inend + "; prestart = " + prestart + "; preend = " + preend);

if (prestart > preend || instart > inend ||

prestart < 0 || prestart >= pre.length || preend < 0 || preend >= pre.length ||

instart < 0 || instart >= in.length || inend < 0 || inend >= in.length) {

return null;

}

TreeNode root = new TreeNode(pre[prestart]);

if (prestart == preend && instart == inend) {

return root;

}

int in_root = 0;

for (int i = instart; i <= inend; i++) {

if (in[i] == root.val) {

in_root = i;

System.out.println("root = " + in_root);

break;

}

}

root.left = recur(pre, in, instart, in_root - 1, prestart + 1, prestart + 1 + (in_root - 1 - instart));

root.right = recur(pre, in, in_root + 1, inend, preend - (inend - in_root - 1), preend);

return root;

}

public void testBuild() {

int[] in = {1,2};

int[] post = {1,2};

TreeNode root = buildTree(in, post);

}

}