uva-699 The Falling Leaves

本文探讨了如何解决一个特定的二叉树问题——计算在每一列上的数值总和,模拟树叶从树上落下并堆积的过程。通过构建二叉树模型,并使用数组记录每列的数值总和,最终输出每列的数值。

摘要生成于 C知道 ,由 DeepSeek-R1 满血版支持, 前往体验 >

Each year, fall in the North Central region is accompanied by the brilliant colors of the leaves on the trees, followed quickly by the falling leaves accumulating under the trees. If the same thing happened to binary trees, how large would the piles of leaves become?


We assume each node in a binary tree "drops" a number of leaves equal to the integer value stored in that node. We also assume that these leaves drop vertically to the ground (thankfully, there's no wind to blow them around). Finally, we assume that the nodes are positioned horizontally in such a manner that the left and right children of a node are exactly one unit to the left and one unit to the right, respectively, of their parent. Consider the following tree:

The nodes containing 5 and 6 have the same horizontal position (with different vertical positions, of course). The node containing 7 is one unit to the left of those containing 5 and 6, and the node containing 3 is one unit to their right. When the "leaves" drop from these nodes, three piles are created: the leftmost one contains 7 leaves (from the leftmost node), the next contains 11 (from the nodes containing 5 and 6), and the rightmost pile contains 3. (While it is true that only leaf nodes in a tree would logically have leaves, we ignore that in this problem.)

Input 

The input contains multiple test cases, each describing a single tree. A tree is specified by giving the value in the root node, followed by the description of the left subtree, and then the description of the right subtree. If a subtree is empty, the value -1 is supplied. Thus the tree shown above is specified as 5 7 -1 6 -1 -1 3 -1 -1. Each actual tree node contains a positive, non-zero value. The last test case is followed by a single -1 (which would otherwise represent an empty tree).

Output 

For each test case, display the case number (they are numbered sequentially, starting with 1) on a line by itself. On the next line display the number of "leaves" in each pile, from left to right, with a single space separating each value. This display must start in column 1, and will not exceed the width of an 80-character line. Follow the output for each case by a blank line. This format is illustrated in the examples below.

Sample Input 

5 7 -1 6 -1 -1 3 -1 -1
8 2 9 -1 -1 6 5 -1 -1 12 -1
-1 3 7 -1 -1 -1
-1

Sample Output 

Case 1:
7 11 3

Case 2:
9 7 21 15
题目意思:给出一棵树,求在每一列的数的和是多少;
解题思路:先把树建好,然后用一个够大的数组把每列的和求出来,最后遍历数组输出。
我想过计算每个节点到最左边的孩子的距离来当数组下标,可实在想不出来怎么实现,大神如果会,请留言……
#include<iostream>
#include<cstring>

using namespace std;

struct node
{
    int data;
    int index;
    node*left,*right;
    node(int a):data(a),index(0),left(0),right(0) {}
};

node* create()
{
    int num;
    cin>>num;
    if(num==-1)
        return 0;
    node*root=new node(num);
    root->left=create();
    root->right=create();
    return root;
}
int arr[10000];
void see(node*root,int index)
{
    if(root)
    {
        //cout<<root->data<<endl;
        arr[index]+=root->data;
        see(root->left,index-1);
        see(root->right,index+1);
    }
}
int main()
{
    int cas=0;
    node* root;
    while(root=create())
    {
        memset(arr,0,sizeof(arr));
        int index=100;
        see(root,index);
        while(arr[index])index--;
        cout<<"Case "<<++cas<<":"<<endl;
        for(index++; arr[index]; index++)
        {
            cout<<arr[index];
            if(arr[index+1])cout<<" ";
        }
        cout<<endl<<endl;
    }
    return 0;
}


<think>好的,我现在需要处理用户的问题:“User-Agent: falling back to 'libdnf': could not detect OS or basearch”。用户之前询问过关于Yocto构建中的dnf错误,现在这个新问题似乎与dnf在检测操作系统或基础架构时失败有关。我需要先理解这个错误的具体原因,然后给出解决方案。 首先,这个错误信息提到User-Agent回退到libdnf,无法检测OS或basearch。根据之前的经验,Yocto项目中使用dnf作为包管理器时,可能会因为系统信息未被正确设置而导致此类问题。可能的原因包括: 1. **缺少必要的元数据**:Yocto构建环境中可能没有正确设置DISTRO或MACHINE变量,导致dnf无法确定操作系统类型和架构。 2. **配置错误**:local.conf或发行版配置文件中的相关设置不正确,比如PACKAGE_ARCH或TARGET_OS。 3. **缓存问题**:之前的构建缓存可能损坏,导致dnf无法正确读取信息。 4. **版本兼容性问题**:libdnf或相关库的版本与Yocto版本不兼容,导致检测失败。 5. **环境变量未正确导出**:构建环境中必要的变量未被正确传递到dnf。 接下来,我需要验证这些可能的原因并找到对应的解决方法。例如,检查local.conf中的DISTRO和MACHINE设置,确认PACKAGE_ARCH是否正确,清理构建缓存,更新元数据层,确保libdnf和相关组件的版本兼容性。另外,查看构建日志中的具体错误信息可以帮助定位问题。 用户之前的问题是关于do_rootfs阶段的dnf调用失败,这次的问题可能与之相关,但更具体于OS和架构检测。需要确保Yocto正确配置了目标系统的信息,以便dnf能够正确识别和操作。可能还需要检查是否缺少必要的包组或配置,比如packagegroup-core-buildessential是否被包含,以确保构建环境完整。 此外,用户可能需要更新Yocto的层(如meta-openembedded)到最新版本,以修复已知的兼容性问题。如果用户之前尝试过清理缓存,可能需要更彻底的清理步骤,或者检查磁盘空间是否足够,避免因资源不足导致的问题。 总结来说,解决步骤可能包括检查配置文件、清理缓存、更新元数据层、验证环境变量,以及查阅详细日志定位具体错误。需要分步骤引导用户逐一排查,确保每个可能的因素都被考虑到,并提供具体的命令和配置示例,帮助用户解决问题。</think>--- ### **错误解析** 错误信息: $$ \text{User-Agent: falling back to 'libdnf': could not detect OS or basearch} $$ 表明包管理工具(如`dnf`或`libdnf`)在尝试确定操作系统类型(OS)或基础架构(basearch,如`x86_64`、`aarch64`)时失败,导致回退到默认行为。此问题常见于**Yocto/OE构建环境**或**自定义Linux发行版构建**中,根源在于系统元数据未被正确传递到包管理器。 --- ### **1. 核心原因** - **缺失元数据**:构建系统未明确指定`DISTRO`(发行版标识)或`MACHINE`(硬件架构)。 - **配置错误**:`local.conf`中`PACKAGE_ARCH`或`TARGET_OS`未正确定义。 - **环境变量未传递**:构建过程中关键变量(如`ARCH`、`DISTRO_NAME`)未被包管理器读取。 - **缓存损坏**:临时文件(如`tmp/`)残留旧数据干扰检测逻辑。 - **软件版本冲突**:`libdnf`版本与构建环境不兼容。 --- ### **2. 分步解决方案** #### **步骤1:检查基础配置** 在Yocto的`conf/local.conf`中确认以下关键配置: ```bash # 指定目标硬件架构(如x86-64、ARM) MACHINE = "qemux86-64" # 定义发行版名称(如poky、自定义名称) DISTRO = "poky" # 确保包架构与目标一致 PACKAGE_ARCH = "${TUNE_PKGARCH}" ``` #### **步骤2:显式定义OS和basearch** 若自动检测失败,在`local.conf`中手动指定: ```bash # 定义目标操作系统类型(如linux) TARGET_OS = "linux" # 强制指定基础架构(如x86_64) BASEARCH = "x86_64" ``` #### **步骤3:清理构建缓存** 删除残留的临时文件和缓存: ```bash # 清理当前配方的缓存 bitbake -c cleanall <image-name> # 彻底删除tmp目录(谨慎操作!) rm -rf tmp/ ``` #### **步骤4:验证环境变量传递** 确保构建环境变量被正确传递到`dnf`。在`local.conf`中添加调试输出: ```bash # 在do_rootfs任务中打印关键变量 addtask do_rootfs after do_debug_vars do_debug_vars() { bbplain "DEBUG: TARGET_OS = ${TARGET_OS}" bbplain "DEBUG: BASEARCH = ${BASEARCH}" bbplain "DEBUG: MACHINE = ${MACHINE}" } ``` #### **步骤5:更新元数据层** 若问题由版本冲突引起,更新相关层(如`meta-openembedded`): ```bash cd sources/meta-openembedded git fetch origin git checkout <stable-branch> # 如kirkstone、mickledore ``` --- ### **3. 扩展排查** #### **检查libdnf兼容性** - 查看`libdnf`版本是否与Yocto版本匹配。例如: ```bash bitbake -s | grep libdnf ``` 若版本过旧,在`conf/local.conf`中指定新版: ```bash PREFERRED_VERSION_libdnf = "0.70.0%" ``` #### **添加必要包组** 确保镜像包含基础包管理支持: ```bash IMAGE_INSTALL:append = " packagegroup-core-boot packagegroup-core-ssh-openssh" ``` #### **检查日志定位问题** 查看`do_rootfs`任务的详细日志: ```bash cat tmp/work/<arch>/<image>/temp/log.do_rootfs | grep -i "detect OS" ``` 关注以下关键词: - `Failed to parse OS release` → `/etc/os-release`文件缺失或格式错误。 - `Unknown architecture` → `BASEARCH`未正确定义。 --- ### **4. 手动修复OS检测** 若自动生成`/etc/os-release`失败,可手动创建补丁: 1. 编写`os-release`文件模板(保存为`files/os-release`): ```bash NAME="${DISTRO_NAME}" VERSION="${DISTRO_VERSION}" ID=${DISTRO} PRETTY_NAME="${DISTRO_NAME} ${DISTRO_VERSION}" ``` 2. 在配方中追加安装任务: ```bash do_install:append() { install -d ${D}${sysconfdir} install -m 0644 ${WORKDIR}/os-release ${D}${sysconfdir}/ } ``` --- ### **5. 验证修复** 重新构建镜像并观察是否仍报错: ```bash bitbake <image-name> ``` --- ### **总结** 此错误通常由**元数据缺失**或**环境配置错误**导致。优先检查`MACHINE`、`DISTRO`和`PACKAGE_ARCH`定义,清理缓存后逐步排查。若问题持续,可通过日志分析具体失败点,必要时手动定义OS和架构参数。
评论
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值