二叉树的数组实现

递归建立二叉树，中序遍历。。。。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define N 10000

int l[N], r[N], key[N], flag;

void insert(int index, int x)
{
    if(x <= key[index])
    {
        if(l[index] == -1)    l[index] = flag;
        else    insert(l[index], x);
    }
    else
    {
        if(r[index] == -1)    r[index] = flag;
        else     insert(r[index], x);
    }
}

void preorder(int index)
{
    if(l[index] != -1)    preorder(l[index]);
    printf("%d ",key[index]);
    if(r[index] != -1)    preorder(r[index]);
}

int main()
{
    int x, root, n;
    memset(l, -1, sizeof(l));
    memset(r, -1, sizeof(r));
    scanf("%d",&n);
    root = -1; flag = 0;
    while(n--)
    {
        scanf("%d", &x);
        if(root == -1)    key[++root] = x;
        else
        {
            key[++flag] = x;
            insert(root, x);
        }
    }
    preorder(root);
    return 0;
}