LeetCode LeetCode Algorithm # Title Solution Difficulty 680 Valid Palindrome II Java , Editorial Easy 678 Valid Parenthesis String Java , Editorial Medium 666 Path Sum IV Java , Discuss Medium 663 Equal Tree Partition Java Medium 662 Maximum Width of Binary Tree Java Medium 661 Image Smoother Java Easy 660 Remove 9 Java Hard 657 Judge Route Circle Java Easy 653 Two Sum IV - Input is a BST Java , Editorial Easy 650 2 Keys Keyboard Java Medium 647 Palindromic Substrings Java Medium 605 Can Place Flowers Java , Editorial Easy 599 Minimum Index Sum of Two Lists Java , Editorial Easy 598 Range Addition II Java , Editorial Easy 594 Longest Harmonious Subsequence Java , Editorial Easy 593 Valid Square Java , Editorial Medium 587 Erect the Fence Java , Editorial Hard 566 Reshape the Matrix Java , Editorial Easy 563 Binary Tree Tilt Java , Editorial Easy 561 Array Partition I Java , Editorial Easy 520 Detect Capital C， C++ Easy 518 Coin Change 2 Java Medium 516 Longest Palindromic Subsequence Java Medium 507 Perfect Number Java , Editorial Easy 494 Target Sum Java Medium 486 Predict the Winner Java Medium 475 Heaters Java Easy 454 4Sum II Java Medium 438 Find All Anagrams in a String Java Easy 421.5 Maximum Xor Secondary Java, Blog --- 421 Maximum XOR of Two Numbers in an Array Java Medium 416 Partition Equal Subset Sum Java Medium 392 Is Subsequence Java Medium 377 Combination Sum IV Java Medium 338 Counting Bits Java Medium 312 Burst Balloons Java Hard 242 Valid Anagram Java, Editorial Easy 167 Two Sum II - Input array is sorted Java, Editorial Easy 91 Decode Ways Java Medium 76 Minimum Window Substring Java Hard 43 Multiply Strings Java Medium 42 Trapping Rain Water Java , Editorial Hard 30 Substring with Concatenation of All Words Java Hard 23 Merge K Sorted Lists Java , Editorial Hard 21 Merge Two Sorted Lists Java Easy 18 4Sum Java Medium 16 3Sum Closest Java Medium 15 3Sum Java Medium 13 Roman to Integer Java Easy 12 Integer to Roman Java Medium 5 Longest Palindromic Substring Java , Go , Editorial Medium 4 Median of Two Sorted Arrays Java , Go , Editorial Hard 3 Longest Substring Without Repeating Characters Java , Go , Editorial Medium 2 Add Two Numbers Java , Go , Editorial Medium 1 Two Sum Java , Go , Editorial Easy