c语言创建二叉树遇到的问题

c语言想用括号表示法创建一个二叉树"A(B(D,E),C(F,G))"
但是不知道为什么运行代码元素C一直添加不进去，求解答

#pragma once
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<assert.h>
#include<math.h>

typedef char TreeDataType;
typedef struct TreeNode
{
    TreeDataType data;
    struct TreeNode* left;
    struct TreeNode* right;
}TreeNode;

TreeNode* createTree(char* str, int* index);
TreeNode* createBinaryTree(char* str);
void PreOrder(TreeNode* root);

TreeNode* createTree(char* str, int* index) 
{
    if (str[*index] == '\0') 
    {
        return NULL;
    }
    if (str[*index] == ')')
    {
        (*index)++;
        return NULL;
    }
    TreeNode* newNode = (TreeNode*)malloc(sizeof(TreeNode));
    newNode->data = str[*index];
    newNode->left = NULL;
    newNode->right = NULL;
    (*index)++;
    if (str[*index] == '(') 
    {
        (*index)++;
        newNode->left = createTree(str, index); 
    }
    if (str[*index] == ',' || str[*index] == '(')
    {
        (*index)++;
        newNode->right = createTree(str, index);
    }
    (*index)++;
    return newNode;
}

TreeNode* createBinaryTree(char* str)
{
    int index = 0;
    return createTree(str, &index);
}
void PreOrder(TreeNode* root)
{
    if (root == NULL)
    {
        return;
    }
    else
    {
        printf("%c ", root->data);
        PreOrder(root->left);
        PreOrder(root->right);
    }
}
int main()
{
    char str[] = "A(B(D,E),C(F,G))";
    TreeNode* root = createBinaryTree(str);
    PreOrder(root);
    return 0;
}

按 TreeNode* createTree(char* str, int* index); 函数写法，构造字符串修改如下，改动处见注释，供参考:

#pragma once
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<assert.h>
#include<math.h>

typedef char TreeDataType;
typedef struct TreeNode
{
    TreeDataType data;
    struct TreeNode* left;
    struct TreeNode* right;
}TreeNode;

TreeNode* createTree(char* str, int* index);
TreeNode* createBinaryTree(char* str);
void PreOrder(TreeNode* root);

TreeNode* createTree(char* str, int* index) //A(B(D),E)),C(F),G))
{
    if (str[*index] == '\0')
    {
        return NULL;
    }
    if (str[*index] == ')')
    {
        (*index)++;
        return NULL;
    }
    TreeNode* newNode = (TreeNode*)malloc(sizeof(TreeNode));
    newNode->data = str[*index];
    newNode->left = NULL;
    newNode->right = NULL;
    (*index)++;
    if (str[*index] == '(')
    {
        (*index)++;
        newNode->left = createTree(str, index); 
    }
    if (str[*index] == ',') // || str[*index] == '(') 修改
    {
        (*index)++;
         newNode->right = createTree(str, index);
    }
    (*index)++;
    return newNode;
}

TreeNode* createBinaryTree(char* str)
{
    int    index = 0;
    return createTree(str, &index);
}
void PreOrder(TreeNode* root)
{
    if (root == NULL)
    {
        return;
    }
    else
    {
        printf("%c ", root->data);
        PreOrder(root->left);
        PreOrder(root->right);
    }
}
void InOrder(TreeNode* root)
{
    if (root == NULL)
        return;
    InOrder(root->left);
    printf("%c ", root->data);
    InOrder(root->right);
}
void PostOrder(TreeNode* root)
{
    if (root == NULL)
        return;
    PostOrder(root->left);
    PostOrder(root->right);
    printf("%c ", root->data);
}


int main()
{
    char str[] = "A(B(D),E)),C(F),G))"; // 修改
    //char str[] = "A(B(D,E),C(F,G))";
    TreeNode* root = createBinaryTree(str);
    PreOrder(root); printf("\n");
    InOrder(root);  printf("\n");
    PostOrder(root);
    return 0;
}

该回答引用ChatGPT

从代码来看,问题出现在createTree函数的这两句:
c

if (str[*index] == ',' || str[*index] == '(')
{
    (*index)++;
    newNode->right = createTree(str, index);
}

这里判断右子树的条件是遇到','或者'(',但是实际上在字符串"A(B(D,E),C(F,G))"中,右子树C的开头是')',不满足这个判断条件,所以C一直添加不进去。
解决方法是:修改判断右子树的条件,增加')'的判断,修改为:
c

if (str[*index] == ',' || str[*index] == '(' || str[*index] == ')')
{
    (*index)++;
    newNode->right = createTree(str, index);
}

完整代码

#pragma once
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<assert.h>
#include<math.h>

typedef char TreeDataType;
typedef struct TreeNode
{
    TreeDataType data;
    struct TreeNode* left;
    struct TreeNode* right;
}TreeNode;

TreeNode* createTree(char* str, int* index);
TreeNode* createBinaryTree(char* str); 
void PreOrder(TreeNode* root);
void InOrder(TreeNode* root);
void PostOrder(TreeNode* root);

TreeNode* createTree(char* str, int* index) 
{
    if (str[*index] == '\0')
    {
        return NULL;
    }
    if (str[*index] == ')')
    {
        (*index)++;
        return NULL;
    }
    TreeNode* newNode = (TreeNode*)malloc(sizeof(TreeNode));
    newNode->data = str[*index];
    newNode->left = NULL;
    newNode->right = NULL;
    (*index)++;
    if (str[*index] == '(')
    {
        (*index)++; 
        newNode->left = createTree(str, index);
    }
    if (str[*index] == ',' || str[*index] == '(' || str[*index] == ')') 
    {
        (*index)++;
        newNode->right = createTree(str, index);
    }
    (*index)++;
    return newNode;
}

TreeNode* createBinaryTree(char* str)
{
    int index = 0;
    return createTree(str, &index);
}

void PreOrder(TreeNode* root)
{
    if (root == NULL)
    {
        return;
    }
    else
    {
        printf("%c ", root->data);
        PreOrder(root->left);
        PreOrder(root->right);
    }
}

void InOrder(TreeNode* root)
{
    if (root == NULL)
    {
        return; 
    }
    else
    {
        InOrder(root->left);
        printf("%c ", root->data);
        InOrder(root->right);
    }
}

void PostOrder(TreeNode* root)
{
    if (root == NULL)
    {
        return;
    }
    else
    {
        PostOrder(root->left);     
        PostOrder(root->right);
        printf("%c ", root->data);
    }
}

int main()
{
    char str[] = "A(B(D,E),C(F,G))";
    TreeNode* root = createBinaryTree(str);
    printf("先序遍历:");
    PreOrder(root);
    printf("\n");
    printf("中序遍历:");
    InOrder(root); 
    printf("\n");
    printf("后序遍历:");
    PostOrder(root);
    printf("\n");
    return 0;
}
运行结果:
先序遍历:A B D E C F G
中序遍历:D B E A F C G
后序遍历:D E B F G C A

问题在于当处理完左子树 B(D,E) 后，程序没有正确的处理逗号后面的 C(F,G)。

要解决这个问题，可以在创建二叉树的时候，先判断当前的字符是否为 ','，如果是的话，就将 index 值自增然后再处理接下来的字符。更改后的 createTree 函数的代码如下所示：

TreeNode* createTree(char* str, int* index) 
{
    if (str[*index] == '\0') 
    {
        return NULL;
    }
    if (str[*index] == ')')
    {
        (*index)++;
        return NULL;
    }
    TreeNode* newNode = (TreeNode*)malloc(sizeof(TreeNode));
    newNode->data = str[*index];
    newNode->left = NULL;
    newNode->right = NULL;
    (*index)++;
    if (str[*index] == '(') 
    {
        (*index)++;
        newNode->left = createTree(str, index); 
    }
    if (str[*index] == ',' || str[*index] == '(')
    {
        (*index)++;
        newNode->right = createTree(str, index);
    }
    // 如果当前字符是逗号，则将 index 值自增
    if (str[*index] == ',')
    {
        (*index)++;
    }
    (*index)++;
    return newNode;
}

修改后的代码可以解决元素 C 无法添加的问题，将程序运行结果输出为 A B D E C F G。