leetcode binary tree loader

main.c

// create by annidy
// 2016-05-13
#include <stdio.h>
#include <utlist.h>
#include <string.h>
#include <stdlib.h>

struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

typedef struct el {
    struct TreeNode *n;
    int    used;    // every n must used 2 times!
    struct el *next;
} el;

int count(char *str)
{
    int n = 0;
    while (*str) {
        if (*str++ == ',')
            n++;
    }
    return n+1;
}

/// user free return
struct TreeNode *loader(char *str) {
    el *head = NULL;
    el *subhead  = NULL;
    el *tmp;
    el *elt;
    
    size_t len = strlen(str);
    char *tstr = malloc(len);
    memcpy(tstr, str+1, len-2);
    tstr[len-2] = 0;
    
    int i = 0;
    char *val = strtok(tstr, ",");
    if (!val) {
        return NULL; // []
    }
    struct TreeNode *tns = calloc(count(str), sizeof(struct TreeNode));
    for (; val; val = strtok(NULL, ","), i++) {
        struct TreeNode *tn = NULL;
        if (strcmp(val, "null") != 0) {
            tns[i].val = atoi(val);
            tn = &tns[i];
            
            // enqeue this to sub list
            el *sub = calloc(1, (sizeof(struct el)));
            sub->n = tn;
            LL_APPEND(subhead, sub);
        }
        
        if (i > 0) {
            if (head->used++ == 0) {
                head->n->left = tn;
            } else {
                head->n->right = tn;
                // used twice now! pop it
                tmp = head->next;
                free(head);
                head = tmp;
            }
        }
        
        if (head == NULL) { // if head empty, swap sub to head
            tmp = subhead;
            subhead = head;
            head = tmp;
        }
    }
    
    LL_FOREACH_SAFE(subhead,elt,tmp) {
        LL_DELETE(subhead,elt);
        free(elt);
    }
    
    return tns;
}