#define S2
struct TreeNode
{
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

#ifdef S1

#include <limits.h>
#include <stdbool.h>
#include <stdlib.h>

struct list_t
{
    int *data;
    size_t idx;
    size_t capacity;

    void (*append)(struct list_t *, int);
    void (*delete)(struct list_t *);
};

void append(struct list_t *self, int v)
{
    if (self->idx >= self->capacity)
    {
        self->data = (int *)realloc(self->data, sizeof(int) * (self->capacity + 5));
        self->capacity += 5;
    }

    self->data[self->idx++] = v;
}

void delete(struct list_t *self)
{
    free(self->data);
    self->idx = 0;
    self->capacity = 0;
}

void init_list(struct list_t *list)
{
    if (!list)
        return;

    list->data = (int *)malloc(sizeof(int) * 5);
    list->capacity = 5;
    list->idx = 0;

    list->append = &append;
    list->delete = &delete;
}

void inorder(struct TreeNode *n, struct list_t *l)
{
    if (!n)
    {
        l->append(l, INT_MIN);
        return;
    }

    if (n->left || n->right)
    {
        inorder(n->left, l);
        l->append(l, n->val);
        inorder(n->right, l);
    }
    else
        l->append(l, n->val);
}

bool cmp(struct list_t l)
{
    int s1 = 0, s2 = l.idx - 1;

    for (; s1 < s2; s1++, s2--)
    {
        if (l.data[s1] != l.data[s2])
            return false;
    }
    return true;
}

bool isSymmetric(struct TreeNode *root)
{
    struct list_t l;
    bool ret;

    init_list(&l);
    inorder(root, &l);
    ret = cmp(l);

    l.delete(&l);
    return ret;
}

#endif

#ifdef S2
#include <stdbool.h>

bool recur(struct TreeNode *l, struct TreeNode *r)
{
    if (!l && !r)
        return true;
    if (!l || !r || l->val != r->val)
        return false;

    return recur(l->left, r->right) && recur(l->right, r->left);
}

bool isSymmetric(struct TreeNode *root)
{
    return !root || recur(root->left, root->right);
}
#endif

int main()
{
    return 0;
}