Return the minimum, maximum, mean, median, and mode of the sample respectively, as an array of floating point numbers.  The mode is guaranteed to be unique.

(Recall that the median of a sample is:

• The middle element, if the elements of the sample were sorted and the number of elements is odd;
• The average of the middle two elements, if the elements of the sample were sorted and the number of elements is even.)

Example 1:

Input: count = [0,1,3,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
Output: [1.00000,3.00000,2.37500,2.50000,3.00000]

Example 2:

Input: count = [0,4,3,2,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
Output: [1.00000,4.00000,2.18182,2.00000,1.00000]

Constraints:

1. count.length == 256
2. 1 <= sum(count) <= 10^9
3. The mode of the sample that count represents is unique.
4. Answers within 10^-5 of the true value will be accepted as correct.

Solution: TreeMap

Time complexity: O(1)
Space complexity: O(1)

// Author: Huahua
class Solution {
public:
  vector<double> sampleStats(vector<int>& count) {
    int counts = 0;
    int minVal = 255;
    int maxVal = 0;
    int mode = -1;
    int modeCount = 0;
    long sum = 0;
    map<int, int> m;
    for (int i = 0; i <= 255; ++i) {      
      if (!count[i]) continue;
      sum += static_cast<long>(i) * count[i];
      minVal = min(minVal, i);
      maxVal = max(maxVal, i);
      if (count[i] > modeCount) {
        mode = i;
        modeCount = count[i];
      }
      m[counts += count[i]] = i;
    }
    auto it1 = m.lower_bound(counts / 2);
    double median = it1->second;    
    auto it2 = next(it1);
    if (counts % 2 == 0 && it2 != m.end() && it1->first == counts / 2) {  
      median = (median + it2->second) / 2;
    }
    return {minVal, maxVal, static_cast<double>(sum) / counts, median, mode};
  }
};

The post 花花酱 LeetCode 1093. Statistics from a Large Sample appeared first on Huahua's Tech Road.

Given a binary search tree (BST) with duplicates, find all the mode(s) (the most frequently occurred element) in the given BST.

Assume a BST is defined as follows:

• The left subtree of a node contains only nodes with keys less than or equal to the node’s key.
• The right subtree of a node contains only nodes with keys greater than or equal to the node’s key.
• Both the left and right subtrees must also be binary search trees.

For example:
Given BST [1,null,2,2],

1
    \
     2
    /
   2

return [2].

Note: If a tree has more than one mode, you can return them in any order.

Follow up: Could you do that without using any extra space? (Assume that the implicit stack space incurred due to recursion does not count).

Solution1: Recursion w/ extra space

Time complexity: O(n)

Space complexity: O(n)

// Author: Huahua
// Running time: 8 ms
class Solution {
public:
  vector<int> findMode(TreeNode* root) {            
    inorder(root);    
    return ans_;
  }
private:
  int val_ = 0;
  int count_ = 0;  
  int max_count_ = 0;
  vector<int> ans_;
  
  void inorder(TreeNode* root) {
    if (root == nullptr) return;
    inorder(root->left);
    visit(root->val);
    inorder(root->right);
  }
  
  void visit(int val) {
    if (count_ > 0 && val == val_) {
      ++count_;   
    } else {
      val_ = val;
      count_ = 1;
    }
    
    if (count_ > max_count_) {
      max_count_ = count_;
      ans_.clear();
    }
    
    if (count_ == max_count_)
      ans_.push_back(val);
  }
};

Solution2: Recursion w/o extra space

Two passes. First pass to find the count of the mode, second pass to collect all the modes.

Time complexity: O(n)

Space complexity: O(1)

// Author: Huahua
// Running time: 8 ms
class Solution {
public:
  vector<int> findMode(TreeNode* root) {            
    inorder(root);    
    mode_count_ = max_count_;    
    count_ = 0;
    inorder(root);
    return ans_;
  }
private:
  int val_ = 0;
  int count_ = 0;
  int mode_count_ = INT_MAX;
  int max_count_ = 0;
  vector<int> ans_;
  
  void inorder(TreeNode* root) {
    if (root == nullptr) return;
    inorder(root->left);
    visit(root->val);
    inorder(root->right);
  }
  
  void visit(int val) {
    if (count_ > 0 && val == val_) {
      ++count_;      
    } else {
      val_ = val;
      count_ = 1;
    }
    
    if (count_ > max_count_)
      max_count_ = count_;
    
    if (count_ == mode_count_)
      ans_.push_back(val);
  }
};

The post 花花酱 LeetCode 501. Find Mode in Binary Search Tree appeared first on Huahua's Tech Road.