根据后续编译和中序遍历构建二叉树

后续遍历最后一个节点即为根节点；中序编译根节点又将二叉树分为左右两颗二叉树

后序遍历（左孩子->右孩子->父节点）

中序遍历（左孩子->父节点->右孩子）

typedef struct node{
        char val;
        struct node *left;
        struct node *right;

}Node;


Node *buildTree(vector<char>&post,vector<char>middle)
{
    if(post.size() != middle.size() || middle.empty())
    {
        return nullptr;
    }
    char ch = post[post.size() -1];
    
    Node* root = new Node();
    root->val = ch;
    root->left = nullptr;
    root->right = nullptr;

    // 构建左子树
    vector<char> leftMiddleNodes;
    vector<char> leftPostNodes;
    set<char>setLeft;
    int index = 0;
    for(; index < middle.size(); ++index)
    {
        if(middle[index] == ch)
        {
            index ++;
            break;
        }
        leftMiddleNodes.push_back(middle[index]);
        setLeft.insert(middle[index]);
    }
    for(auto &ch : post)
    {
        if(setLeft.find() != setLeft.end())
        {
            leftPostNodes.push_back(ch);
        }
    }
    root->left = buildTree(leftPostNodes,leftMiddleNodes);
    // 构建右子树
    vector<char> rightMiddleNodes;
    vector<char> rightPostNodes;
    set<char>setright;
    for(; index < middle.size(); ++index)
    {
        rightMiddleNodes.push_back(middle[index]);
        setright.insert(middle[index]);
    }
    for(auto &ch : post)
    {
        if(setright.find() != setright.end())
        {
            rightPostNodes.push_back(ch);
        }
    }
    root->right = buildTree(rightPostNodes,rightMiddleNodes);
    return root;
}