LeetCode: Populating Next Right Pointers in Each Node II

LeetCode: Populating Next Right Pointers in Each Node II 

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import static org.junit.Assert.assertSame;
/**
 * Created by hzhou on 4/27/15. [email protected]
 * <p/>
 * https://chazyhabit.wordpress.com/2014/08/16/populating-next-right-pointers-in-each-node-ii-leetcode-83/
 */
public class PopulatingNextRightPointersInEachNodeII {
    public void connect(TreeLinkNode root) {
        if (root == null) {
            return;
        }
        TreeLinkNode head = null; // the head node of the next level
        TreeLinkNode prev = null; // the previous node of the current node in the same level
        TreeLinkNode curr = root;
        while (curr != null) {
            while (curr != null) {
                if (curr.left != null) {
                    if (prev == null) {
                        head = curr.left;
                    } else {
                        prev.next = curr.left;
                    }
                    prev = curr.left;
                }
                if (curr.right != null) {
                    if (prev == null) {
                        head = curr.right;
                    } else {
                        prev.next = curr.right;
                    }
                    prev = curr.right;
                }
                curr = curr.next;
            }
            // go to next level
            curr = head;
            head = null;
            prev = null;
        }
    }
    @Test
    public void test() {
        TreeLinkNode root = new TreeLinkNode(1);
        root.left = new TreeLinkNode(2);
        root.right = new TreeLinkNode(3);
        root.left.left = new TreeLinkNode(4);
        root.left.right = new TreeLinkNode(5);
        root.right.right = new TreeLinkNode(7);
        connect(root);
        assertSame(root.left.right.next, root.right.right);
    }
}