Data Structure Binary Tree: Lowest Common Ancestor in a Binary Tree

http://www.geeksforgeeks.org/lowest-common-ancestor-binary-tree-set-1/

 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <queue>
 #include <stack>
 #include <string>
 #include <fstream>
 #include <map>
 using namespace std;

 struct node {
     int data;
     struct node *left, *right;
     node() : data(), left(NULL), right(NULL) { }
     node(int d) : data(d), left(NULL), right(NULL) { }
 };

 bool findpath(node *root, vector<int> &path, int n) {
     if (!root) return false;
     path.push_back(root->data);
     if (root->data == n) return true;
     if (root->left && findpath(root->left, path, n) || root->right && findpath(root->right, path, n)) return true;
     path.pop_back();
     return false;
 }

 int LCA(node *root, int n1, int n2) {
     if (!root) return -;
     vector<int> path1, path2;
     if (!findpath(root, path1, n1) || !findpath(root, path2, n2)) return -;
     int i = ;
     for (; i < path1.size() && i < path2.size(); i++) {
         if (path1[i] != path2[i]) break;
     }
     return path1[i-];
 }

 int main() {
     node *root = new node();
     root->left = new node();
     root->right = new node();
     root->left->left = new node();
     root->left->right = new node();
     root->right->left = new node();
     root->right->right = new node();
     cout << "LCA(4, 5) is " << LCA(root, , ) << endl;
     cout << "LCA(4, 6) is " << LCA(root, , ) << endl;
     cout << "LCA(3, 4) is " << LCA(root, , ) << endl;
     cout << "LCA(2, 4) is " << LCA(root, , ) << endl;
     return ;
 }

one traversal

 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <queue>
 #include <stack>
 #include <string>
 #include <fstream>
 #include <map>
 using namespace std;

 struct node {
     int data;
     struct node *left, *right;
     node() : data(), left(NULL), right(NULL) { }
     node(int d) : data(d), left(NULL), right(NULL) { }
 };

 node* LCA(node *root, int n1, int n2) {
     if (!root) return NULL;
     if (root->data == n1 || root->data == n2) return root;
     node *l = LCA(root->left, n1, n2);
     node *r = LCA(root->right, n1, n2);
     if (l && r) return root;
     return l? l : r;
 }

 int main() {
     node *root = new node();
     root->left = new node();
     root->right = new node();
     root->left->left = new node();
     root->left->right = new node();
     root->right->left = new node();
     root->right->right = new node();
     cout << "LCA(4, 5) is " << LCA(root, , )->data << endl;
     cout << "LCA(4, 6) is " << LCA(root, , )->data << endl;
     cout << "LCA(3, 4) is " << LCA(root, , )->data << endl;
     cout << "LCA(2, 4) is " << LCA(root, , )->data << endl;
     return ;
 }

上面这段代码有些问题，当n1或者n2不存在时应该回NULL，但是回的是n1或者n2

 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <queue>
 #include <stack>
 #include <string>
 #include <fstream>
 #include <map>
 using namespace std;

 struct node {
     int data;
     struct node *left, *right;
     node() : data(), left(NULL), right(NULL) { }
     node(int d) : data(d), left(NULL), right(NULL) { }
 };

 node* _LCA(node *root, int n1, int n2, bool &v1, bool &v2) {
     if (!root) return NULL;
     if (root->data == n1) {
         v1 = true;
         return root;
     }
     if (root->data == n2) {
         v2 = true;
         return root;
     }
     node *l = _LCA(root->left, n1, n2, v1, v2);
     node *r = _LCA(root->right, n1, n2, v1, v2);
     if (l && r) return root;
     return l? l : r;
 }

 bool findnode(node *root, int k) {
     if (!root) return false;
     return (root->data == k || findnode(root->left, k) || findnode(root->right, k));
 }

 node *LCA(node *root, int n1, int n2) {
     bool v1 = false;
     bool v2 = false;
     node *lca = _LCA(root, n1, n2, v1, v2);
     if (v1 && v2 || v1 && findnode(root, n2) || v2 && findnode(root, n1)) return lca;
     return NULL;
 }

 int main() {
     node *root = new node();
     root->left = new node();
     root->right = new node();
     root->left->left = new node();
     root->left->right = new node();
     root->right->left = new node();
     root->right->right = new node();
     cout << "LCA(4, 5) is " << LCA(root, , )->data << endl;
     cout << "LCA(4, 6) is " << LCA(root, , )->data << endl;
     cout << "LCA(3, 4) is " << LCA(root, , )->data << endl;
     cout << "LCA(2, 4) is " << LCA(root, , )->data << endl;
     return ;
 }