Question

我正在尝试在二叉搜索树中实现插入子例程，其中每个节点都有一个单词（字符串）作为键。我从STDIN中取出单词并使用insert函数插入它们。但每当我进行顺序遍历时，我发现树不会超过3个节点。有什么不对？我的代码附在此处：

typedef struct treenode
{
  char word[20];             //word is the key for each node
  struct treenode *left;
  struct treenode *right;

} treenode;



treenode *insert (treenode *node, char *word)   
{   
  if(node==NULL)                       //if a null node is reached,make a temp node and append it
  {
    treenode *temp;
    temp = (treenode *) malloc(sizeof(treenode));
    strcpy (temp ->word,word);
    temp-> left = NULL;
    temp-> right = NULL;
    return temp;
   }


    if ((strcmp(word, node ->word)>0))  //if the key is greater than node.word,go to right child
    {
        node-> right = insert(node-> right, word);
    }
    else if(strcmp(word,node->word)<=0)  //if key <node.word,go to left child
    {
        node-> left = insert(node-> left, word); 
    }

}

void printinorder(treenode *node)
{

   if(node == NULL) return;
   printinorder(node-> left);
   printf("%s ",node-> word);
   printinorder(node-> right);

}



int main()
{
    treenode *root = NULL;
    char string[20];
    scanf("%s",string);  //first input is taken once here and once again inside loop,but its OK
    root = insert(root, string+1);  //duplicate entries are also stored

    while(strcmp(string,".")!=0)   //input is terminated by a full stop
    {
        insert(root, string+1); 
        scanf("%s",string);
    }


    printinorder(root);           //finally printing the BST
    return 0;
}

Answer 1

您的实现问题在于您尝试将create_node和insert组合到一个函数中，然后将该单个函数用作树的“一刀切”解决方案初始化和插入。这引起了insert返回类型的并发症（如评论中所述），可能会导致您错过insert中所需的递归。（注意 else和insert代码下的tree->right中添加了tree->left

最好将create_node和insert例程拆分为单独的函数。这样就可以将create_node定义为类型treenode，将insert定义为类型void。这简化了每个代码，使逻辑更容易，更易读。这样，您的代码就会变成：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct treenode
{
char word[20];             //word is the key for each node
struct treenode *left;
struct treenode *right;

} treenode;

treenode* create_node (char *word)
{
    treenode* tmp = malloc (sizeof (struct treenode));
    if (tmp) {
        strcpy (tmp ->word,word);
        tmp->left = NULL;
        tmp->right = NULL;
    } else {
        fprintf (stderr, "%s() error: memory exhausted\n", __func__);
    }
    return tmp;
}

void insert (treenode *tree, char *word)
{

    if (strcmp (word, tree->word) > 0)
    {
        if (tree->right == NULL) {
            tree->right = create_node (word);
            insert (tree->right, word);
        } else {
            insert (tree->right, word);
        }
    }
    else if (strcmp (word, tree->word) < 0)
    {
        if (tree->left == NULL) {
            tree->left = create_node (word);
            insert (tree->left, word);
        } else {
            insert (tree->left, word);
        }
    }
}

void printinorder(treenode *node)
{
    if(node == NULL) return;
    printinorder(node-> left);
    printf("%s ",node-> word);
    printinorder(node-> right);
}

int main()
{
    treenode *root = NULL;
    char string[20];
    scanf ("%s",string);  //first input is taken once here and once again inside loop,but its OK
    root = create_node (string);  //duplicate entries are also stored

    while (strcmp (string,".")!=0)   //input is terminated by a full stop
    {
        insert (root, string); 
        scanf ("%s",string);
    }

    printinorder(root);           //finally printing the BST

    return 0;
}

<强>建立/运行：

$ gcc -Wall -Wextra -o bst bst.c
$ ./bst
my_dog
has
fleas
my_cat
likes
snakes
.
fleas has likes my_cat my_dog snakes

另外，正如评论中所述 - 不要投射malloc 。这是不必要的，并增加了出错的可能性。

树不会超过3号

1 个答案: