530. 二叉搜索树的最小绝对差
class Solution {
private:
int result = INT_MAX;
TreeNode* pre = NULL;
void traversal(TreeNode* cur){
if (cur == NULL) return;
traversal(cur->left); //左
if(pre != NULL){ //中
result = min(result, cur->val - pre->val);
}
pre = cur;
traversal(cur->right); //右
}
public:
int getMinimumDifference(TreeNode* root) {
traversal(root);
return result;
}
};
501.二叉搜索树中的众数
class Solution {
private:
int maxCount = 0;
int count = 0;
TreeNode* pre = NULL;
vector<int> result;
void searchBST(TreeNode* cur){
if(cur == NULL) return;
searchBST(cur->left); //左
//中
if(pre == NULL){
count = 1;
}
else if(pre->val == cur->val){
count++;
}
else{ // pre != NULL && pre->val != cur->val
count = 1;
}
pre = cur; //移动指针
if(count == maxCount){
result.push_back(cur->val);
}
if(count > maxCount){
maxCount = count;
result.clear();
result.push_back(cur->val);
}
searchBST(cur->right); //右
return;
}
public:
vector<int> findMode(TreeNode* root) {
count = 0;
maxCount = 0;
pre = NULL;
result.clear();
searchBST(root);
return result;
}
};
236.二叉树的最近公共祖先
class Solution {
public:
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
if(root == q || root == p || root == NULL) return root;
TreeNode* left = lowestCommonAncestor(root->left, p ,q); //左
TreeNode* right = lowestCommonAncestor(root->right, p, q); //右
//中
if(left != NULL && right != NULL) return root;
if(left == NULL && right != NULL) return right;
else if(left != NULL && right == NULL) return left;
else{ // (left == NULL && right == NULL)
return NULL;
}
}
};