【前缀码判定c++程序】求帮助，测试用例出现无效内存引用，不知道问题出在哪里

#include<iostream>
#include<cstdio>
#include<malloc.h>
#include<string.h>
//构建哈夫曼树来判定是否有重复的二叉树路径
typedef struct BiTCode{                  // 结点结构
    int flag;
    struct BiTCode *Left, *Right; // 左右孩子指针
}BiTCode;

int main()
{
    int n;
    scanf("%d",&n);
   
    BiTCode *Root;
    Root=(BiTCode *)malloc(sizeof(BiTCode));
    Root->flag = 0;
    Root->Left = NULL;
    Root->Right = NULL;
   
    for(int i=0;i<n;i++)            //   iiiii,循环读取n个字符串
    {
        char str[1000]="";
        scanf("%s",&str);
        
        int len;
        len=strlen(str);
        
        BiTCode *p;
        p= Root;
        for(int j=0;j<len;j++)        //    jjjjj，读取当前字符串的每一位
        {
            if(str[j]=='0')
            {
                if( (p->Left)==NULL )
                {
                    p->Left =(BiTCode *)malloc(sizeof(BiTCode));
                    p = p->Left;
                    p->Left  = NULL;
                    p->Right = NULL;
                    if (j == len - 1)
                    {                //读到最后一个字符
                        p->flag = 1;//将在此停止的放置标记为1
                    }
                    else
                    {                //将路上遍历过的节点都设置成为0
                        p->flag = 0;
                    }
                }else
                {
                    if( (j==len-1)||(p->Left->flag) )//当前读取的字符串的最后一位或者有字符串在这里结束
                    {
                        printf("%s\n",str);
                        return 0;
                    }else
                    {
                        p=p->Left;
                    }
                }
            }
            //右边
            if(str[j]=='1')
            {
                if( (p->Right)==NULL )
                {
                    p->Right =(BiTCode *)malloc(sizeof(BiTCode));
                    p = p->Right;
                    p->Left  = NULL;
                    p->Right = NULL;
                    if (j == len - 1)
                    {                //读到最后一个字符
                        p->flag = 1;//将在此停止的放置标记为1
                    }
                    else
                    {                //将路上遍历过的节点都设置成为0
                        p->flag = 0;
                    }
                }else
                {
                    if( (j==len-1)||(p->Right->flag) )//当前读取的字符串的最后一位或者有字符串在这里结束
                    {
                        printf("%s\n",str);
                        return 0;
                    }else
                    {
                        p=p->Right;
                    }
                }
            }
        }
    }
    printf("YES\n");
    return 0;
}