add prob #235

Author: randomwalk10

235_Lowest_Common_Ancestor_of_a_Binary_Search_Tree.cpp

@@ -0,0 +1,69 @@
+/*
+Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
+
+According to the definition of LCA on Wikipedia: The lowest common ancestor is defined between two nodes p and qas the lowest node in T that has both p and qas descendants (where we allow a node to be a descendant of itself).
+
+Given binary search tree: root =[6,2,8,0,4,7,9,null,null,3,5]
+
+
+
+
+Example 1:
+
+Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
+Output: 6
+Explanation: The LCA of nodes 2 and 8 is 6.
+Example 2:
+
+Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
+Output: 2
+Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.
+
+
+Note:
+
+All of the nodes' values will be unique.
+p and q are different and both values willexist in the BST.
+
+来源：力扣（LeetCode）
+链接：https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-search-tree
+著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
+*/
+
+#define NULL 0
+
+struct TreeNode {
+ int val;
+ TreeNode *left;
+ TreeNode *right;
+ TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+};
+
+class Solution {
+	private:
+		TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q,
+				bool& is_p, bool& is_q){
+			is_p = (root==p)?true:false; is_q = (root==q)?true:false;
+			if(root==NULL) return NULL;
+			TreeNode* res;
+			// left
+			bool is_p_l, is_q_l;
+			res = lowestCommonAncestor(root->left, p, q, is_p_l, is_q_l);
+			is_p |= is_p_l; is_q |= is_q_l;
+			if(res) return res;
+			else if(is_p&&is_q) return root;
+			// right
+			bool is_p_r, is_q_r;
+			res = lowestCommonAncestor(root->right, p, q, is_p_r, is_q_r);
+			is_p |= is_p_r; is_q |= is_q_r;
+			if(res) return res;
+			else if(is_p&&is_q) return root;
+			// return
+			return NULL;
+		}
+	public:
+		TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
+			bool is_p, is_q;
+			return lowestCommonAncestor(root, p, q, is_p, is_q);
+		}
+};