已知二叉树以二叉链表存储，编写算法完成：对于树种每个元素值为x的结点，删除以它为根的子树，并释放相应的空间

#include <iostream>
#include <queue>
typedef struct treenode{char data;struct treenode *left;struct treenode *right;
}treenode,*ptreenode;ptreenode buytreenode(char x)
{ptreenode n=(ptreenode) malloc(sizeof (treenode));n->data=x;n->left= nullptr,n->right= nullptr;return n;
}
ptreenode build_tree()
{ptreenode root= buytreenode('A');root->left= buytreenode('B');root->right= buytreenode('C');root->left->left= buytreenode('D');root->left->right= buytreenode('E');root->right->left= buytreenode('F');root->right->right= buytreenode('G');root->left->left->left= buytreenode('H');root->left->left->right= buytreenode('I');return root;
}void free_tree(ptreenode root)//后序释放节点
{if(root== nullptr) return;free_tree(root->left);free_tree(root->right);free(root);
}ptreenode free_x(ptreenode root,char x)
{if(root== nullptr) return nullptr;if(root->data==x) {free_tree(root);return nullptr;}root->left=free_x(root->left,x);root->right=free_x(root->right,x);}void print_tree(ptreenode root)
{std::queue<ptreenode > tmp;tmp.push(root);int s=tmp.size();while(!tmp.empty()){ptreenode t=tmp.front();tmp.pop();s--;printf("%3c",t->data);if(t->left) tmp.push(t->left);if(t->right) tmp.push(t->right);if (s==0) puts(""),s=tmp.size();}
}
int main() {ptreenode root=build_tree();print_tree(root);ptreenode tmp= free_x(root,'B');puts("");print_tree(tmp);return 0;
}