1. LeetCode 230
Given the root of a binary search tree, and an integer k, return the kth smallest value (1-indexed) of all the values of the nodes in the tree.
Example 1:
Input: root = [3,1,4,null,2], k = 1 Output: 1
Example 2:
Input: root = [5,3,6,2,4,null,null,1], k = 3 Output: 3
Constraints:
- The number of nodes in the tree is n.
- 1 <= k <= n <= 104
- 0 <= Node.val <= 104
Follow up: If the BST is modified often (i.e., we can do insert and delete operations) and you need to find the kth smallest frequently, how would you optimize?
2. LeetCode 380
Implement the RandomizedSet class:
- RandomizedSet() Initializes the RandomizedSet object.
- bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present, false otherwise.
- bool remove(int val) Removes an item val from the set if present. Returns true if the item was present, false otherwise.
- int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned.
You must implement the functions of the class such that each function works in average O(1) time complexity.
Example 1:
Input ["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"] [[], [1], [2], [2], [], [1], [2], []] Output [null, true, false, true, 2, true, false, 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set, returns true. Set now contains [1,2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set, returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set, so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set, getRandom() will always return 2.
Constraints:
- -231 <= val <= 231 - 1
- At most 2 * 105 calls will be made to insert, remove, and getRandom.
- There will be at least one element in the data structure when getRandom is called.
3. LeetCode 1034
You are given an m x n integer matrix grid, and three integers row, col, and color. Each value in the grid represents the color of the grid square at that location.
Two squares belong to the same connected component if they have the same color and are next to each other in any of the 4 directions.
The border of a connected component is all the squares in the connected component that are either 4-directionally adjacent to a square not in the component, or on the boundary of the grid (the first or last row or column).
You should color the border of the connected component that contains the square grid[row][col] with color.
Return the final grid.
Example 1:
Input: grid = [[1,1],[1,2]], row = 0, col = 0, color = 3 Output: [[3,3],[3,2]]
Example 2:
Input: grid = [[1,2,2],[2,3,2]], row = 0, col = 1, color = 3 Output: [[1,3,3],[2,3,3]]
Example 3:
Input: grid = [[1,1,1],[1,1,1],[1,1,1]], row = 1, col = 1, color = 2 Output: [[2,2,2],[2,1,2],[2,2,2]]
Constraints:
- m == grid.length
- n == grid[i].length
- 1 <= m, n <= 50
- 1 <= grid[i][j], color <= 1000
- 0 <= row < m
- 0 <= col < n
