235. 二叉搜索树的最近公共祖先
class Solution {
TreeNode* dfs(TreeNode* root, TreeNode* p, TreeNode* q){
if(root==NULL){
return root;
}
if(root->val>p->val&&root->val>q->val){
TreeNode*left = dfs(root->left,p,q);
if(left!=NULL){
return left;
}
}
if(root->val<p->val&&root->val<q->val){
TreeNode*right = dfs(root->right,p,q);
if(right!=NULL){
return right;
}
}
return root;
}
public:
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
return dfs(root,p,q);
}
};
239. 滑动窗口最大值
class MyQueue {
deque<int>que;
public:
void push(int x) {
while(!que.empty()&&que.back()<x){
que.pop_back();
}
que.push_back(x);
}
void pop(int x){
if(!que.empty()&&que.front()==x){
que.pop_front();
}
}
int front(){
return que.front();
}
};
class Solution {
public:
vector<int> maxSlidingWindow(vector<int>& nums, int k) {
MyQueue que;
vector<int>res;
for(int i=0;i<k;i++){
que.push(nums[i]);
}
res.push_back(que.front());
for(int i=k,j=0;i<nums.size();i++,j++){
que.pop(nums[j]);
que.push(nums[i]);
res.push_back(que.front());
}
return res;
}
};
347.前 K 个高频元素
class Solution {
public:
static bool cmp(pair<int,int>&a,pair<int,int>&b){
return a.second>b.second;
}
vector<int> topKFrequent(vector<int>& nums, int k) {
unordered_map<int,int>mp;
vector<int>res;
for(unsigned int i = 0;i<nums.size();i++){
mp[nums[i]]++;
}
vector<pair<int,int>>vec(mp.begin(),mp.end());
sort(vec.begin(),vec.end(),cmp);
for(int i=0;i<k;i++){
res.push_back(vec[i].first);
}
return res;
}
};