taixingbi

Combination.py

https://leetcode.com/problemset/all/?search=Combination%20Sum
candidates without duplicates: 39 / 
                                      78 sub sets / 254. Factor Combinations
                                                  
candidates with duplicates: 40 / 267. Palindrome Permutation II
combinations of k numbers: 216
output number of possible combinations:  377 
others： 10. Regular Expression Matching / 294. Flip Game II / 291. Word Pattern II / 51. N-Queens /52. N-Queens II / 351. Android Unlock Patterns

taixingbi

Structured Query Language(SQL)
*basic
. JOIN 
  FROM table1 JOIN table2 ON table1.col= table1.col
  
  INNER: at least one match of rows
  LEFT: match left table rows
  RIGHT: match right table rows
  FULL: matching rows in both tables
       

taixingbi

1. Correlation
https://en.wikipedia.org/wiki/Correlation_coefficient
+1 strongest possible agreement
0 two varaible are independent 
−1 strongest possible disagreement

r(x,y)= cov(x,y)/(var(x)*var(y))**.5 
---cov(x,y)= E( (x-u)(y-u) )
---var(x) var=  (E(x-u)**2 )

taixingbi

Depth 
1 maximun depth: 104

104. Maximum Depth of Binary Tree
https://leetcode.com/problems/maximum-depth-of-binary-tree/description/

class Solution {
    public int maxDepth(TreeNode root) {
        //O(N)
        if(root==null) return 0;

taixingbi

merge: 617
trim: 669


617. Merge Two Binary Trees
https://leetcode.com/problems/merge-two-binary-trees/description/
Example 1:
Input: 
	Tree 1                     Tree 2                  
          1                         2                             

taixingbi

Level Order Traversal: 102 / 107 / 637
                        /582

102. Binary Tree Level Order Traversal
https://leetcode.com/problems/binary-tree-level-order-traversal/description/
Given binary tree [3,9,20,null,null,15,7],
    3
   / \
  9  20
    /  \

taixingbi

1. Separate chaining
 linked lists of values
  * search time complexity: logn

2. Open addressing
 Insert(k): Keep probing until an empty slot is found. Once an empty slot is found, insert k.
 Search(k): Keep probing until slot’s key doesn’t become equal to k or an empty slot is reached.
  *  linear probing
 

taixingbi

973. K Closest Points to Origin
https://leetcode.com/problems/k-closest-points-to-origin/
We have a list of points on the plane.  Find the K closest points to the origin (0, 0).
(Here, the distance between two points on a plane is the Euclidean distance.)
You may return the answer in any order.  The answer is guaranteed to be unique (except for the order that it is in.)
Example 1:
Input: points = [[1,3],[-2,2]], K = 1
Output: [[-2,2]]
Explanation: 
The distance between (1, 3) and the origin is sqrt(10).

taixingbi

237. Delete Node in a Linked List
https://leetcode.com/problems/delete-node-in-a-linked-list/description/
class Solution(object):
    def deleteNode(self, node):
        """
        :type node: ListNode
        :rtype: void Do not return anything, modify node in-place instead.
        """
        if not node:    return
        node.val= node.next.val

taixingbi

516. Longest Palindromic Subsequence
https://leetcode.com/problems/longest-palindromic-subsequence/
https://www.youtube.com/watch?v=v8irqkTcJ6s
Given a string s, find the longest palindromic subsequence's length in s. You may assume that the maximum length of s is 1000.
Example 1:
Input:
"bbbab"
Output:
4
One possible longest palindromic subsequence is "bbbb".