Least Common Ancestor of two nodes in a Given Unordered Tree.

There can be three possibilities for finding LCA is a tree.
1. Both nodes belong to left sub-tree.
2. Both nodes belong to right sub-tree.
3. One per each sub-tree.
 In fact 4th possibility is also there, i.e. nodes are not at all present in the tree.

In the first case, Current node can't be the LCA because an CA exist in the left sub-tree.
Similarly, in the second case, Current node can't be the LCA because an CA exist in the right sub-tree.
In the third case, Current node will be the LCA.

struct node{
 int data;
 struct node* left;
 struct node* right;
};

struct node* leastCommonAncestor(struct node* root,struct node* p,struct node* q){
 
 if(root==NULL){
  return NULL;  //If no root  leastCommonAncestor is NULL.
 }

 if(root==p || root==q){
  return root; // Check if the current root is equal to any of the desired node.
 }else{
  struct node* l=leastCommonAncestor(root->left, p, q); // Find LCA in left of the tree
  struct node* r=leastCommonAncestor(root->right, p, q); // Find LCA in right of the tree
  
  if(l!=NULL && r!=NULL){
   return root; 
  }else if(l!=NULL && r==NULL){
   return l;
  }else if(l==NULL && r!=NULL){
   return r;
  }else{
   return NULL;
  }
 } 
}