https://leetcode.com/problems/largest-odd-number-in-string/description/

Return the largest valued odd integer that is a non-empty substring of a given string num. If no odd integer exists, return an empty string.

https://leetcode.com/problems/construct-string-from-binary-tree/description/

606. Construct String from Binary Tree

Given the root of a binary tree, construct a string consisting of parenthesis and integers using the preorder traversal. Omit all unnecessary empty parenthesis pairs that do not affect the one-to-one mapping relationship between the string and the original binary tree.

Example 1:

Input: root = [1,2,3,4]
Output: "1(2(4))(3)"
Explanation: Originally, it needs to be "1(2(4)())(3()())", but you need to omit all the unnecessary empty parenthesis pairs. And it will be "1(2(4))(3)"

Example 2:

Input: root = [1,2,3,null,4]
Output: "1(2()(4))(3)"
Explanation: Almost the same as the first example, except we cannot omit the first parenthesis pair to break the one-to-one mapping relationship between the input and the output.

Constraints:

- The number of nodes in the tree is in the range [1, 104].
- Node.val is between -1000 and 1000.

https://leetcode.com/problems/binary-tree-inorder-traversal/description/

Binary Tree Inorder Traversal - Given the root of a binary tree, return the inorder traversal of its nodes' values.

https://leetcode.com/problems/transpose-matrix/description/

Transpose 2D matrix

https://leetcode.com/problems/element-appearing-more-than-25-in-sorted-array/description/

Most frequent element

https://leetcode.com/problems/maximum-product-of-two-elements-in-an-array/description/

Maximum Product of Two Elements in an Array

https://leetcode.com/problems/special-positions-in-a-binary-matrix/description/

Number of single 1 in row/col matrix

https://leetcode.com/problems/difference-between-ones-and-zeros-in-row-and-column/description/

diff[i][j] = onesRowi + onesColj - zerosRowi - zerosColj

https://leetcode.com/problems/destination-city/description/

Destination city in a paths[i] = [cityAi, cityBi] path

https://leetcode.com/problems/valid-anagram/description/

Are two strings an anagram

Yearly badge

https://leetcode.com/problems/design-a-food-rating-system/description/

Given foods, cuisines and ratings implement efficient methods changeRating(food, newRating) and highestRated(cuisine)

https://leetcode.com/problems/maximum-product-difference-between-two-pairs/description/

max * second_max - min * second_min

https://leetcode.com/problems/image-smoother/description/

3x3 average of each cell in 2D matrix

https://leetcode.com/problems/buy-two-chocolates/description/

Money change after two chocolates bought

https://leetcode.com/problems/widest-vertical-area-between-two-points-containing-no-points/description/

Max x window between xy points

https://leetcode.com/problems/maximum-score-after-splitting-a-string/description/

Max left_zeros + right_ones in 01-array

https://leetcode.com/problems/path-crossing/description/

Is path string of 'N', 'E', 'W', 'S' crosses

https://leetcode.com/problems/minimum-changes-to-make-alternating-binary-string/description/

Minimum operations to make 01-string with no two adjacent equal

https://leetcode.com/problems/decode-ways/description/

Ways to decode back 'A' -> '1', 'B' -> '2' … 'Z' -> '26'

https://leetcode.com/problems/number-of-dice-rolls-with-target-sum/description/

Ways to throw once n dices with k faces to make target sum.