二叉搜索树递归插入

时间:2011-10-26 08:50:56

标签: c++ recursion binary-search-tree

我目前在使用递归将节点插入二叉树时遇到困难。我一直在研究这个问题几天,并且认为是时候我来寻找答案了!

节点类(.h):

#ifndef STUDENT_MACROGUARD
#define STUDENT_MACROGUARD

#include <cstdlib>
#include <string>

namespace student_class
{
    class student
    {
        public:
            // Constructors / Destructors;

            student(const float entry = 0, std::string name = "", 
                        student* left_ptr = NULL, student* right_ptr = NULL);
            ~student(void){};

            // Mutating member functions;

            void set_grade(const float entry);
            void set_name(std::string entry);

            void set_left(student* node_ptr);
            void set_right(student* node_ptr);

            // Non mutating member functions;

            float grade(void);
            std::string name(void);

            student* left(void);
            student* right(void);

            // Const member functions;

            const student* left(void) const;
            const student* right(void) const;

    private:
            std::string student_name;
            float grade_field;
            student* left_ptr;
            student* right_ptr;
    };
}

#endif

BSTree类实现二叉树数据结构(.h):

#ifndef BTTree_MACROGUARD
#define BTTree_MACROGUARD

#include <cstdlib>
#include <string>
#include <iostream>
#include "student.h"

using namespace student_class;

namespace BTTree_class
{
class BTTree
{
    public:
            // Constructors / Destructors; 

            BTTree(student* node_ptr = NULL);
            ~BTTree(void);

            // Mutating member functions;

            void insert(student* node_ptr = NULL, const float grade = 0, std::string name = "");
            void remove(student* node_ptr);

            // Non mutating member functions;

            student* grade_search(const float entry);
            student* name_search(const std::string entry);
            student* root(void);
            void print_tree(student* node_ptr);

            // Const member functions;

            const student* grade_search(const float entry) const;
            const student* name_search(const float entry) const;
            const student* root(void) const;

    private:
            student* root_ptr;
    };
}

#endif

我用来将节点插入树中的插入成员函数实现:

    void BTTree::insert(student* node_ptr, const float grade, std::string name)
{
    if(root_ptr == NULL)
    {
        root_ptr = new student(grade, name);
        return;
    }

    if(node_ptr == NULL)
    {
        node_ptr = new student(grade, name);
        return;
    }
    else if(node_ptr->grade() > grade)
    {
        insert(node_ptr->left(), grade, name);
    }
    else
    {
        insert(node_ptr->right(), grade, name);
    }
}

我不明白为什么这个插入不起作用。代码看起来完美无瑕,让我摸不着头脑。我编写了一个使用迭代的替代插入函数,但递归是必须的。

任何帮助都会很棒,谢谢。

1 个答案:

答案 0 :(得分:3)

问题在于:

if(node_ptr == NULL)
{
    node_ptr = new student(grade, name);
    return;
}

node_ptr是一个局部变量,因为你按值传递它。因此,退出函数时,分配将丢失。

要修复它 - 按参考传递:

void BTTree::insert(student* &node_ptr, const float grade, std::string name)

这当然需要这些改变:

        student* & left(void);
        student* & right(void);