601 
Human Traffic of Stadium 
Hard 

605 
Can Place Flowers 
Easy 

606 
Construct String from Binary Tree 
Easy 
String

Tree

609 
Find Duplicate File in System 
Medium 

611 
Valid Triangle Number 
Medium 

617 
Merge Two Binary Trees 
Easy 
Tree

621 
Task Scheduler 
Medium 

622 
Design Circular Queue 
Medium 

623 
Add One Row to Tree 
Medium 
Tree

628 
Maximum Product of Three Numbers 
Easy 

629 
K Inverse Pairs Array 
Hard 

630 
Course Schedule III 
Hard 

632 
Smallest Range Covering Elements from K Lists 
Hard 

633 
Sum of Square Numbers 
Medium 

636 
Exclusive Time of Functions 
Medium 

637 
Average of Levels in Binary Tree 
Easy 
Tree

638 
Shopping Offers 
Medium 

639 
Decode Ways II 
Hard 

640 
Solve the Equation 
Medium 

641 
Design Circular Deque 
Medium 

643 
Maximum Average Subarray I 
Easy 

645 
Set Mismatch 
Easy 

646 
Maximum Length of Pair Chain 
Medium 

647 
Palindromic Substrings 
Medium 

648 
Replace Words 
Medium 

649 
Dota2 Senate 
Medium 

650 
2 Keys Keyboard 
Medium 

652 
Find Duplicate Subtrees 
Medium 
Tree

653 
Two Sum IV  Input is a BST 
Easy 
Tree

654 
Maximum Binary Tree 
Medium 
Tree

655 
Print Binary Tree 
Medium 
Tree

657 
Robot Return to Origin 
Easy 

658 
Find K Closest Elements 
Medium 

659 
Split Array into Consecutive Subsequences 
Medium 

661 
Image Smoother 
Easy 

662 
Maximum Width of Binary Tree 
Medium 
Tree

663 
Equal Tree Partition 
Medium 
Tree

664 
Strange Printer 
Hard 

665 
Nondecreasing Array 
Medium 

666 
Path Sum IV 
Medium 
Tree

667 
Beautiful Arrangement II 
Medium 

668 
Kth Smallest Number in Multiplication Table 
Hard 

669 
Trim a Binary Search Tree 
Medium 
Tree

670 
Maximum Swap 
Medium 

671 
Second Minimum Node In a Binary Tree 
Easy 
Tree

672 
Bulb Switcher II 
Medium 

673 
Number of Longest Increasing Subsequence 
Medium 

674 
Longest Continuous Increasing Subsequence 
Easy 

684 
Redundant Connection 
Medium 

685 
Redundant Connection II 
Hard 

687 
Longest Univalue Path 
Medium 
Tree

Recursion

700 
Search in a Binary Search Tree 
Easy 
Tree
