二叉树——在二叉树中找到一个节点的前驱节点

二叉树——在二叉树中找到一个节点的后继节点

可以将该结点分为两种情况，

1.没有左子树，那它是某一个结点的右子树的最左结点，然后找到这个右子树的parent即可

　　找它的parent，直到当前节点是parent的右子树为止

2.有左子树，那前驱节点就是它的左子树的最右结点

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;
        }
    }

　　

测试代码

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);
    }