二叉搜索树中的前序遍历

Question

我运行遇到了问题，无法弄清楚为什么我的方法在找到时 return 没有对象？它首先递归遍历树的左侧，然后再遍历右侧。 println 语句在找到客户时打印，但 return customer 始终是 null。我在这里做错了什么？

    public Customer lookUpCustomer(String lastName, String firstName) {

    Customer customer;
    Customer foundCustomer = null;

    if (left != null) {

        customer = (Customer) left.getItem();

        if(customer.getLastName().equals(lastName) && customer.getFirstName().equals(firstName)) {
            System.out.println("Found customer: " + customer.toString());
            return customer;
            //foundCustomer = customer;             
        }
        left.lookUpCustomer(lastName, firstName);
    }
    if (right != null) {

        customer = (Customer) right.getItem();

        if(customer.getLastName().equals(lastName) && 
       customer.getFirstName().equals(firstName)) {
            System.out.println("Found customer: " + customer.toString());
            return customer;
            //foundCustomer = customer;         
        }   
        right.lookUpCustomer(lastName, firstName);
    }

    return null;
}

Answer 1

因为您总是 returning null 第一次调用 lookUpCustomer 函数。此外，您没有从 lookUpCustomer 方法的递归调用中保存 returned 值。

解决这个return找到的节点。您可以按如下方式更改代码：

public Customer lookUpCustomer(String lastName, String firstName) {

    Customer customer;
    Customer foundCustomer = null;

    if (left != null) {

        customer = (Customer) left.getItem();

        if(customer.getLastName().equals(lastName) && customer.getFirstName().equals(firstName)) {
            System.out.println("Found customer: " + customer.toString());
            return customer;
            //foundCustomer = customer;             
        }
        foundCustomer = left.lookUpCustomer(lastName, firstName);
    }
    if (foundCustomer==null && right != null) {

        customer = (Customer) right.getItem();

        if(customer.getLastName().equals(lastName) && 
       customer.getFirstName().equals(firstName)) {
            System.out.println("Found customer: " + customer.toString());
            return customer;
            //foundCustomer = customer;         
        }   
        foundCustomer  = right.lookUpCustomer(lastName, firstName);
    }

    return foundCustomer;
}

二叉搜索树中的前序遍历

Preorder traversing in Binary Search Tree

java

traversal