在C中的双链表中添加子项

Question

I have a struct defined as:

struct ac {
    int value;
    char character; 
    char * word;
    struct ac *next;
    struct ac *previous;
    struct ac *child;
    struct ac *parent;
};

I specifically have a problem when a word contains the same character twice or more at the end of the word.

// 'w' is the word input
int depth = 0;
ac *a; // is struct that is size of ac and contains all of the struct values set either to NULL or 0.
while(w[depth] != '\0'){
    if (a -> character == w[depth]) {
        if ((a -> value == 0) && (w[depth +1] == '\0')) {
            a -> value = 1;
            a -> word = malloc(strlen(w)+1);
            strcpy(a -> word, w);
        }
        printf("follow existing path %c\n", w[depth]);
        a = a -> child;
        depth ++;
    }
// word() is a function that reserves memory for the new word and initializes new_word problaply not relevent for this question.
    else if (a -> child == NULL) {
        new_word = word(w,depth);
        new_word -> parent = a;
        printf("create child %c\n", w[depth]);
        a -> child = new_word;
        a = new_word;
        depth ++;
    }
}

for example, when the word 'well' is the input the following output wil be printed:

• create child w
• create child e
• create child l
• follow existing path l

But this last 'follow existing path l' should have been 'create child l'

and i can't seem to think of a condition that wil discriminate against that last 'l'. Can someone maybe help me with this? it would be much appreciated.

Answer 1

The problem is that you are not looking ahead properly. You should be checking if a->child is NULL first , adding a new node if it is and then moving to that child.

If a->child is not NULL , then you should compare a->child->character to the current character, and move to a->child if it matches.

I think it should look like this:

int depth = 0;
ac *a;
while (w[depth] != '\0') {
    if (a->child == NULL) {
        new_word = word(w,depth);
        new_word->parent = a;
        printf("create child %c\n", w[depth]);
        a->child = new_word;
        a = new_word;
        depth ++;
    }
    else if (a->child->character == w[depth]) {
        if ((a->child->value == 0) && (w[depth +1] == '\0')) {
            a->child->value = 1;
            a->child->word = malloc(strlen(w)+1);
            strcpy(a->child->word, w);
        }
        printf("follow existing path %c\n", w[depth]);
        a = a->child;
        depth ++;
    }
}