Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”
Example 1:
Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1 Output: 3 Explanation: The LCA of nodes 5 and 1 is 3.
Example 2:
Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.
Example 3:
Input: root = [1,2], p = 1, q = 2 Output: 1
Constraints:
[2, 105].-109 <= Node.val <= 109Node.val are unique.p != qp and q will exist in the tree.
class Solution {
public:
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
if(root==NULL) return NULL;
if(root==p) return p;
else if(root==q) return q;
TreeNode* left= lowestCommonAncestor(root->left,p,q);
TreeNode* right= lowestCommonAncestor(root->right,p,q);
if(left and right)return root;
else if(left and !right)return left;
else if(right and !left)return right;
else return NULL;
}
};
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