buildTree.png

  1. 这个题得用后序遍历，用前序遍历删不干净
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public TreeNode pruneTree(TreeNode root) {

        if (root == null) {
            return null;
        }

        root.left = pruneTree(root.left);
        root.right = pruneTree(root.right);

        if (root.left == null && root.right == null && root.val == 0) {
            return null;
        }

        return root;

    }