message: Add note for 646. It's similar to 435.
diff: @@ -744,7 +744,7 @@ I'll keep updating for full summary and better solutions. Stay tuned for updates
  455 | [Assign Cookies](https://leetcode.com/problems/assign-cookies/) | [C++](./C++/assign-cookies.cpp) [Python](./Python/assign-cookies.py) | _O(nlogn)_ | _O(1)_ | Easy | |
  621 | [Task Scheduler](https://leetcode.com/problems/task-scheduler/) | [C++](./C++/task-scheduler.cpp) [Python](./Python/task-scheduler.py) | _O(n)_ | _O(1)_ | Medium | |
  630 | [Course Schedule III](https://leetcode.com/problems/course-schedule-iii/) | [C++](./C++/course-schedule-iii.cpp) [Python](./Python/course-schedule-iii.py) | _O(nlogn)_ | _O(k)_ | Hard ||
  -646 | [Maximum Length of Pair Chain](https://leetcode.com/problems/maximum-length-of-pair-chain/) | [C++](./C++/maximum-length-of-pair-chain.cpp) [Python](./Python/maximum-length-of-pair-chain.py) | _O(nlogn)_ | _O(1)_ | Medium || Scan Line
  +646 | [Maximum Length of Pair Chain](https://leetcode.com/problems/maximum-length-of-pair-chain/) | [C++](./C++/maximum-length-of-pair-chain.cpp) [Python](./Python/maximum-length-of-pair-chain.py) | _O(nlogn)_ | _O(1)_ | Medium || Scan Line. Similar to "435 Non-overlapping Intervals".
  649 | [Dota2 Senate](https://leetcode.com/problems/dota2-senate/) | [C++](./C++/dota2-senate.cpp) [Python](./Python/dota2-senate.py) | _O(n)_ | _O(n)_ | Medium |||
  659 | [Split Array into Consecutive Subsequences](https://leetcode.com/problems/split-array-into-consecutive-subsequences/) | [C++](./C++/split-array-into-consecutive-subsequences.cpp) [Python](./Python/split-array-into-consecutive-subsequences.py) | _O(n)_ | _O(1)_ | Medium | |
  738 | [Monotone Increasing Digits](https://leetcode.com/problems/monotone-increasing-digits/) | [C++](./C++/monotone-increasing-digits.cpp) [Python](./Python/monotone-increasing-digits.py) | _O(1)_ | _O(1)_ | Medium | |
  