如何替换二叉搜索树中的节点

How to replace a node in a binary search tree

本文关键字：搜索树 节点 何替换 替换      更新时间：2023-10-16

我有一个带有字符串的二叉搜索树。每个节点都包含字符串和字符串的频率。

我的函数有两个字符串，s1，s2。我必须用 s1 替换 s2。如果 s2 已经存在于 bstree 中，我只需要添加 s1 的频率。如果它不存在，我创建一个频率为 s1 的新节点。

我所做的是：(1(我从bstree中删除s1并保存s1的频率(2( 我将 s2 插入 bstree(使用 s1 的频率(

问题是当 (1( 工作并且 s1 的节点被删除时第二部分什么也没给我(当我在没有删除功能的情况下运行它时，它会给我一些奇怪的符号(

struct node{
    string data;
    int freq;
    node *left, *right;
    node(string d, int f){
        data = d;
        freq = f;
        left = right = nullptr;
    }
node *replacehelp(node *r, string v, int f){
        if(r == nullptr)
            return new node(v,f);
        int state = v.compare(r->data);//to check the alphabetical order
        if(state == 0){
            r->freq += f;
            return r;
        }
        if(state > 0)
            r->right = replacehelp(r->right, v, f);
        else if(state < 0)
            r->left = replacehelp(r->left, v, f);
    }
void replace(const string &s1, const string &s2){
    //the delete function works(I get the freq of s1)
    root = DeleteNode(root, s1, &freq);
    //I have to insert s2 to the tree
    root = replacehelp(root,s2,freq);
}

您的问题来了，因为替换帮助中缺少返回。

请注意，测试 (state < 0) 在 replacehelp 中是无用的，因为它不是 0 也不是正数，所以

node *replacehelp(node *r, string v, int f){
  if(r == nullptr)
    return new node(v,f);
  int state = v.compare(r->data);//to check the alphabetical order
  if(state == 0)
    r->freq += f; 
  else if(state > 0) // 'else' ADDED
    r->right = replacehelp(r->right, v, f);
  else // MODIFIED
    r->left = replacehelp(r->left, v, f);
  return r;
}

您没有给出DeleteNode的定义，是否不可能知道它是否像您想象的那样正确。

如果我添加一些定义来运行：

#include <iostream>
#include <string>
using namespace std;
struct node{
  string data;
  int freq;
  node *left, *right;
  node(string d, int f){
    data = d;
    freq = f;
    left = right = nullptr;
  }
};
node *replacehelp(node *r, string v, int f){
  if(r == nullptr)
    return new node(v,f);
  int state = v.compare(r->data);//to check the alphabetical order
  if(state == 0)
    r->freq += f;
  else if(state > 0) // 'else' ADDED
    r->right = replacehelp(r->right, v, f);
  else  // MODIFIED
    r->left = replacehelp(r->left, v, f);
  return r; // ADDED
}
// ADDED
node * DeleteNode(node *r, string s, int * freq) // can be "int & freq" to not have to give the addr in the call
{
  if (r != nullptr) {
    int state = s.compare(r->data);
    if (state > 0)
      r->right = DeleteNode(r->right, s, freq);
    else if (state < 0)
      r->left = DeleteNode(r->left, s, freq);
    else {
      *freq = r->freq;
      if (r->right == nullptr) {
        node * t = r->left;
        delete (r);
        return t;
      }
      if (r->left == nullptr) {
        node * t = r->right;
        delete (r);
        return t;
      }
      node * t = r->right;
      while ((t != nullptr) && (t->left != nullptr))
        t = t->left;
      r->data = t->data;
      r->freq = t->freq;
      int dummy;
      r->right = DeleteNode(r->right, t->data, &dummy);
    }
  }
  return r;
}
node * root; // ADDED
void replace(const string &s1, const string &s2){
  int freq = 0; // initialized to 0 to not have undefined value if DeleteNode do not find the node
  //the delete function works(I get the freq of s1)
  root = DeleteNode(root, s1, &freq);
  //I have to insert s2 to the tree
  root = replacehelp(root,s2,freq);
}
// ADDED
void insert(string s, int freq)
{
  root = replacehelp(root, s, freq);
}
// ADDED
void pr(node *r)
{
  cout << '(';
  if (r != nullptr) {
    pr(r->left);
    cout << '"' << r->data << "" " << r->freq;
    pr(r->right);
  }
  cout << ')';
}
// ADDED
int main(void)
{
  insert("5", 5);
  insert("4", 4);
  insert("3", 3);
  insert("6", 6);
  pr(root);
  cout << endl;
  replace("5", "55");
  pr(root);
  cout << endl;
  replace("3", "33");
  pr(root);
  cout << endl;
  replace("4", "33");
  pr(root);
  cout << endl;
}

编译和执行：

pi@raspberrypi:/tmp $ g++ -g -pedantic -Wextra -Werror t.cc
pi@raspberrypi:/tmp $ ./a.out
(((()"3" 3())"4" 4())"5" 5(()"6" 6()))
(((()"3" 3())"4" 4(()"55" 5()))"6" 6())
(((()"33" 3())"4" 4(()"55" 5()))"6" 6())
(((()"33" 7())"55" 5())"6" 6())
pi@raspberrypi:/tmp $
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