剑指Offer-05重建二叉树

public static TreeNode buildTree(int[] preorder, int[] inorder) {
    if (preorder == null || preorder.length == 0 || inorder == null || inorder.length == 0 ){
        return null;
    }
    //前序遍历第一个元素必定是根结点
    TreeNode root = new TreeNode(preorder[0]);
    //标记中序遍历根结点的位置
    int tag = 0;
    for (int i = 0; i < inorder.length; i++){
        if(inorder[i] == root.val){
            tag = i;
            break;
        }
    }
    //中序遍历根结点左边的就构成左子树
    int[] leftTreeI = Arrays.copyOf(inorder, tag);
    //前序遍历也找到左子树
    int[] leftTreeP = Arrays.copyOfRange(preorder, 1, 1 + leftTreeI.length);
    //递归左分支
    root.left = buildTree(leftTreeP, leftTreeI);
    //中序遍历根结点右边的就构成右子树
    int[] rightTreeI = Arrays.copyOfRange(inorder,  tag + 1, inorder.length);
    //前序遍历也找到左子树
    int[] rightTreeP = Arrays.copyOfRange(preorder, preorder.length - rightTreeI.length, preorder.length);
    //递归右分支
    root.right = buildTree(rightTreeP, rightTreeI);
    return root;
}