二叉樹——在二叉樹中找到一個節點的前驅節點

二叉樹——在二叉樹中找到一個節點的后繼節點

可以將該結點分為兩種情況，

1.沒有左子樹，那它是某一個結點的右子樹的最左結點，然后找到這個右子樹的parent即可

　　找它的parent，直到當前節點是parent的右子樹為止

2.有左子樹，那前驅節點就是它的左子樹的最右結點

 

public static Node findPreNode(Node node){
        if(node == null) return null;
        if(node.left == null){
            Node parentNode = node.parent;
            while(parentNode != null && parentNode.right != node){
                node = parentNode;
                parentNode = node.parent;
            }
            return parentNode;
        } else{
            node = node.left;
            while(node.right != null){
                node = node.right;
            }
            return node;
        }
    }

 

　　

 

測試代碼

 

public static void main(String[] args){
        Node node = new Node(1);
        node.left = new Node(2);
        node.right = new Node(3);
        node.left.left = new Node( 4 );
        node.left.right = new Node(5);
        node.right.left = new Node( 6 );
        node.right.right = new Node( 7 );
        node.left.left.left = new Node(11);
        node.left.right.right = new Node( 8 );
        node.right.left.right = new Node(9);
        node.right.right.right = new Node(10);

        node.parent = null;
        node.left.parent = node;
        node.right.parent = node;
        node.left.left.parent = node.left;
        node.left.right.parent = node.left;
        node.right.left.parent = node.right;
        node.right.right.parent = node.right;
        node.left.left.left.parent = node.left.left;
        node.left.right.right.parent = node.left.right;
        node.right.left.right.parent = node.right.left;
        node.right.right.right.parent = node.right.right;

        System.out.println(findPreNode( node.left.right.right ).value);
        System.out.println(findPreNode( node.right.left ).value);
    }