@Test
public void test() {
int[] A = new int[] {0, 1, 0, 0, 4, 0, 5};
int[] B = new int[] {0, 1, 0, 0, 4, 0, 5};
TreeNode root = new TreeNode(A);
TreeNode root2 = new TreeNode(B);
System.out.println(root.printTree());
System.out.println(sinkZerosInBT(root).printTree());
System.out.println(sinkZerosInBT2(root2).printTree());
}
/*
* Recursion. Sink zeros in child subtree first, and then parent.
* time: O(n^2); space: O(1)
*/
public TreeNode sinkZerosInBT(TreeNode root) {
if (root == null) return null;
root.left = sinkZerosInBT(root.left);
root.right = sinkZerosInBT(root.right);
if (root.val == 0) {
TreeNode node = getLowestNonZeroNode(root);
swap(root, node);
}
return root;
}
private void swap(TreeNode root, TreeNode node) {
int tmp = root.val;
root.val = node.val;
node.val = tmp;
}