Q4.6 找到两个结点的第一个共同祖先

Design an algorithm and write code to find the first common ancestor of two nodes in a binary tree. Avoid storing additional nodes in a data structure. NOTE: This is not necessarily a binary search tree.

bool covers(Node *root,Node *p)
{
    if(!root) return false;
    if(root==p) return true;
    return covers(root->left,p)||covers(root->right,p);
}

Node * commonFather(Node *root,Node *p,Node *q)
{
    if(covers(root->left,p)&&covers(root->left,q))
        return commonFather(root->left,p,q);
    if(covers(root->right,p)&&covers(root->right,q))
        return commonFather(root->right,p,q);
    return root;
}