# gopalcdas/Friday-Fun-Session

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 // 17th Jan 2019 (87th) – Common First Ancestor of Two Nodes in a Binary Tree with All Unique Values // https://gopalcdas.com/2017/10/10/topics-in-friday-fun-session/ #include #include #include using namespace std; struct Node { int val; struct Node *l; struct Node *r; }; Node *AddNode(int val) { Node *t = new Node(); t->val = val; t->l = NULL; t->r = NULL; return t; } Node *BuildTree() { Node *root = AddNode(40); root->l = AddNode(30); root->r = AddNode(50); root->l->l = AddNode(10); root->l->r = AddNode(35); root->r->l = AddNode(45); root->r->r = AddNode(80); root->l->l->l = AddNode(11); root->l->l->r = AddNode(12); root->l->r->l = AddNode(33); root->l->r->r = AddNode(37); root->r->l->l = AddNode(41); root->r->l->r = AddNode(48); root->r->r->l = AddNode(60); root->r->r->r = AddNode(200); return root; } int CommonFirstAncestor(Node *root, int f, int s, Node **cp) { if (root == NULL) return 0; int lc = CommonFirstAncestor(root->l, f, s, cp); int rc = CommonFirstAncestor(root->r, f, s, cp); int totalCount = lc + rc + ((root->val == f || root->val == s) ? 1 : 0); if (*cp == NULL && totalCount == 2) *cp = root; return totalCount; } int main() { Node *root = BuildTree(); Node *cp = NULL; CommonFirstAncestor(root, 33, 37, &cp); if (cp == NULL) cout << "not found"; else cout << cp->val << endl; getchar(); return 0; }