平常工作里面基本不用tree,一提到tree总是心虚,多写吧
Binary Search Tree vs Binary Tree
In a binary search tree there is a relative ordering in how the nodes are organized, while there is nothing of that sort in a binary tree. In Binary search tree, all the nodes to the left of a node have values less the value of the node, and all the nodes to the right of a node have values greater than the value of the node.
Leetcode 235. Lowest Common Ancestor of a Binary Search Tree
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)
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
if(root->val < p->val && root->val < q->val)
{
return lowestCommonAncestor(root->right, p, q);
}
if(root->val > p->val && root->val > q->val)
{
return lowestCommonAncestor(root->left, p, q);
}
return root;
}
};
iterative写法:
TreeNode* cur = root;
while(cur)
{
if(cur->val < p->val && cur->val < q->val)
{
cur = cur->right;
}
else if(cur->val > p->val && cur->val > q->val)
{
cur = cur->left;
}
else
{
break;
}
}
return cur;
- Lowest Common Ancestor of a Binary Tree
tree recursive 写的时候到底什么时候该return?
看了别人的能理解,可是自己写的时候似乎总在return那里挣扎,TODO吧
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
if(root == NULL || p == root || q == root) return root;
TreeNode* left = lowestCommonAncestor(root->left, p, q);
TreeNode* right = lowestCommonAncestor(root->right, p, q);
if(left != NULL && right != NULL) return root;
return left != NULL ? left : right;
}
};