1. Problem Statement (Simple Explanation): You’re given a 9×9 Sudoku board (char[9][9]), partially filled. You must determine if the board is valid according to Sudoku rules for the filled cells only : Each row must contain digits 1-9 without repetition . Each column must contain digits 1-9 without repetition . Each of the nine 3×3 sub-boxes must contain digits 1-9 without repetition . Notes: Empty cells are denoted by '.' and can be ignored. A valid board might not be solvable; you only validate current filled cells. 2. Examples: Example 1 (Valid): [["5","3",".",".","7",".",".",".","."] ,["6",".",".","1","9","5",".",".","."] ,[".","9","8",".",".",".",".","6","."] ,["8",".",...
1. Problem Statement (Simple Explanation): You are given: A sorted array nums of distinct integers (ascending). An integer target. You must: Return the index of target in nums if it exists. If not, return the index where target should be inserted to keep the array sorted. You must use an O(log n) algorithm → binary search. 2. Examples: Example 1: Input: nums = [1,3,5,6], target = 5 5 exists at index 2. Output: 2 Example 2: Input: nums = [1,3,5,6], target = 2 Sorted insertion position: 1 (index 0) < 2 3 (index 1) > 2 → 2 should go at index 1. Output: 1 Example 3: Input: nums = [1,3,5,6], target = 7 7 is greater than all elements, so it would be inserted at index 4 (end of array). Output: 4 3. Approach – Binary Search for Lower Bound (O(log n)): We want the smallest index i such that: nums[i] >= target If nums[i] == target, that’s th...