update cheatsheet, readme

Author: yennanliu

README.md

@@ -271,7 +271,7 @@
 723 | [Candy Crush](https://leetcode.com/problems/candy-crush/) | [Python](./leetcode_python/Array/candy-crush.py) | _O((R * C)^2)_ | _O(1)_ | Medium |`complex`| AGAIN (not start)
 724 | [Find Pivot Index](https://leetcode.com/problems/find-pivot-index/) | [Python](./leetcode_python/Array/find-pivot-index.py)  | _O(n)_ | _O(1)_ | Easy || OK*
 729 | [My Calendar I](https://leetcode.com/problems/my-calendar-i/) |  [Python](./leetcode_python/Array/my-calendar-i.py), [Java](./leetcode_java/src/main/java/LeetCodeJava/Array/MyCalendar1.java) | _O(nlogn)_ | _O(n)_ | Medium |good basic, brute force, binary search, google| AGAIN**** (1)
-731 | [My Calendar II](https://leetcode.com/problems/my-calendar-ii/) | [Python](./leetcode_python/Array/my-calendar-ii.py), [Java](./leetcode_java/src/main/java/LeetCodeJava/Array/MyCalendar2.java) | _O(n^2)_ | _O(n)_ | Medium |`trick`, `basic`, google,| AGAIN** (2)
+731 | [My Calendar II](https://leetcode.com/problems/my-calendar-ii/) | [Python](./leetcode_python/Array/my-calendar-ii.py), [Java](./leetcode_java/src/main/java/LeetCodeJava/Array/MyCalendar2.java) | _O(n^2)_ | _O(n)_ | Medium |`trick`, scanning line, google,| AGAIN** (2)
 747 | [Largest Number At Least Twice of Others](https://leetcode.com/problems/largest-number-at-least-twice-of-others/) | [Python](./leetcode_python/Array/largest-number-at-least-twice-of-others.py) | _O(n)_ | _O(1)_ | Easy |`good basic`, `data structure`| OK* 
 755 | [Pour Water](https://leetcode.com/problems/pour-water/) | [Python](./leetcode_python/Array/pour-water.py) | _O(v * n)_ | _O(1)_ | Medium |`complex`| AGAIN (not start)
 766 | [Toeplitz Matrix](https://leetcode.com/problems/toeplitz-matrix/) | [Python](./leetcode_python/Array/toeplitz-matrix.py)  | _O(m * n)_ | _O(1)_ | Easy |`basic`, `matrix`, `google`| AGAIN* (2)

doc/cheatsheet/scanning_line.md

@@ -1,10 +1,24 @@
-# Scanning Line 
+# Scanning Line  (AKA `Line Sweep`)
 
 ## 0) Concept  
-1. Find the "max" overlap in intervals
+
+> Find the "max" overlap in intervals
+
+- https://web.ntnu.edu.tw/~algo/Point2.html
+- https://hackmd.io/@meyr543/SkrRZCwfj
 
 ### 0-1) Types
 
+- Meeting room
+    - LC 253
+    - LC 759
+    - LC 2021
+- Calendar
+    - LC 731
+- Others
+    - LC 1851
+    - LC 218
+
 ### 0-2) Pattern
 ```python
 open_close = []