[Leetcode 105]*前序后序遍历形成树

    public TreeNode find(int[] preorder, int[] inorder,int j, int start, int end) {
        if (j > preorder.length - 1 || start > end) {
            return null;
        }
        TreeNode root = new TreeNode(preorder[j]);
        int flag = 0; 
       
        for (int i = start; i <= end; i++) {
            if (inorder[i] == root.val) {
                flag = i;
            }
        }
        root.left = find(preorder, inorder,j + 1,start, flag - 1);
        root.right = find(preorder, inorder,j + flag - start + 1, flag + 1, end);
        return root;
    }