yangpeng-chn

int findKthLargest(vector<int>& nums, int k) {
    priority_queue<int, vector<int>, greater<int>> pq;
    for (int num : nums) {
        pq.push(num);
        if (pq.size() > k) {
            pq.pop();
        }
    }
    return pq.top();
}

yangpeng-chn

int ceilSearch(int arr[], int low, int high, int x) 
{ 
    if(x <= arr[low]) return low;  
    if(x > arr[high]) return -1;   
    int mid = low + (high - low)/2;
    
    if(arr[mid] == x) 
        return mid; 
            
    /* If x is greater than arr[mid], then either arr[mid + 1] 

yangpeng-chn

int findRight(const ArrayReader& reader, int target){
    int right = 1;
    while (reader.get(right) < target) 
        right = right * 2;
    return right;
}

int searchInfiniteArray(const ArrayReader& reader, int target) {
    int left = 0, right = findRight(reader, target);
     

yangpeng-chn

//Iteration
vector<vector<int>> permute(vector<int>& nums) {
    vector<vector<int>> res;
    queue<vector<int>> q;
    q.push(vector<int>());
    for(auto num : nums){
        // we will take all existing permutations and add the current number to create new
        // permutations
        int n = q.size();
        for(int i = 0; i < n; i++){

yangpeng-chn

void helper(string &s, int l, vector<string> &v){
    if(l == s.size()){
        v.push_back(s);
        return;
    }
    helper(s, l+1, v);
    if(isalpha(s[l])){
        s[l] ^= (1<<5); //toggle upper to lower, lower to upper
        helper(s, l+1, v);
        s[l] ^= (1<<5); //restore, it works without this line, but to leave the origin string unchanged, better to have it.

yangpeng-chn

vector<vector<int>> subsetsWithDup(vector<int>& nums) {
    vector<vector<int>> res{{}}; // same as: vector<vector<int>> res; res.push_back(vector<int>());
    int start = 0, end = 0;
    sort(nums.begin(), nums.end());
    for(int i = 0; i < nums.size(); i++){
        start = 0;
        if(i > 0 && nums[i] == nums[i-1])
            start = end + 1;
            
        end = res.size() - 1;

yangpeng-chn

// Iteration
vector<vector<int>> subsets(vector<int>& nums) {
    vector<vector<int>> vv;
    vv.push_back(vector<int>());
    for(int i = 0; i < nums.size(); i++){
        int n = vv.size();
        for(int j = 0; j < n; j++){
            vector<int> v(vv[j]);
            v.push_back(nums[i]);
            vv.push_back(v);

yangpeng-chn

void helper(TreeNode* root, vector<vector<int>> &res, vector<int>&vec, int sum){
    if(!root)return;
    vec.push_back(root->val);
    if(!root->left && !root->right && root->val==sum)
        res.push_back(vec);
    helper(root->left, res, vec, sum-root->val);
    helper(root->right, res, vec, sum-root->val);
    vec.pop_back();
}
vector<vector<int>> pathSum(TreeNode* root, int sum) {

yangpeng-chn

// Iteration
bool hasPathSum(TreeNode* root, int sum) {
    if(!root) return false;
    stack<TreeNode*>s{{root}};
    while(!s.empty()){
        TreeNode* tmp = s.top();
        s.pop();
        if(!tmp->left && !tmp->right && tmp->val == sum)
            return true;
        if(tmp->left){

yangpeng-chn

// Iteration
vector<vector<int> > levelOrderBottom(TreeNode* root) {
    if (!root) return {};
    vector<vector<int>> res;
    queue<TreeNode*> q{{root}};
    while (!q.empty()) {
        vector<int> oneLevel;
        for (int i = q.size(); i > 0; --i) { //init i with q.size(), it runs well even if we change the size of q in loop
            TreeNode *t = q.front(); 
            q.pop();