设一棵二叉树的结点结构为(LLINK,INFO,RLINK)，ROOT为指向该二叉树根结点的指针，p和q分别为指向该二叉树中任意两个节点的指针，试编写算法ANCESTOR(ROOT,p,q,r)，找到p和q的最近公共祖先结点r

#include <iostream>
#include <stack>
#include<queue>
typedef struct treenode{char INFO;struct treenode *LLINK;struct treenode *RLINK;
}treenode,*ptreenode;ptreenode buytreenode(char x)
{ptreenode n=(ptreenode) malloc(sizeof (treenode));n->INFO=x;n->LLINK= nullptr,n->RLINK= nullptr;return n;
}ptreenode build_tree()
{ptreenode root= buytreenode('A');root->LLINK= buytreenode('B');root->RLINK= buytreenode('C');root->LLINK->LLINK= buytreenode('D');root->LLINK->RLINK= buytreenode('E');root->RLINK->LLINK= buytreenode('F');root->RLINK->RLINK= buytreenode('G');root->LLINK->LLINK->LLINK= buytreenode('H');root->LLINK->LLINK->RLINK= buytreenode('I');return root;
}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->INFO);if (t->LLINK) tmp.push(t->LLINK);if (t->RLINK) tmp.push(t->RLINK);if (s == 0) puts(""), s = tmp.size();}
}ptreenode ancestor(ptreenode root,ptreenode p,ptreenode q)
{if(root==q||root==p||root== nullptr) return root;ptreenode left= ancestor(root->LLINK,p,q);ptreenode right= ancestor(root->RLINK,p,q);if(left!= nullptr&&right!= nullptr) return root;if(left== nullptr) return right;return left;//如果left和right都是空的，那么返回其中任意一个就行，也就是返回空
}
int main() {ptreenode root=build_tree();print_tree(root);puts("");printf("%3c\n",ancestor(root,root->LLINK->LLINK,root->LLINK->RLINK)->INFO);puts("");printf("%3c\n",ancestor(root,root->LLINK->LLINK->LLINK,root->LLINK->LLINK->RLINK)->INFO);return 0;
}