leetcode- Valid Sudoku

https://leetcode.com/problems/valid-sudoku/description/
In a 9 * 9 matrix, check if each numbers (0-9) doesn’t repeat in each row, col and 3 * 3 matrix.

  • use a HashSet or array to check if the number is used.
  • check 3*3 squart –> board [ i + k/3 ][ j + k%3 ] (i, j are 9*9 board index, k is the check board (0-9) index)
  • if(digit > 9 || digit < 1 || check[digit -1]), check digit is valid first then check if the number is used

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LeetCode – Plus One

Given a non-negative integer represented as a non-empty array of digits, plus one to the integer. You may assume the integer do not contain any leading zero, except the number 0 itself. The digits are stored such that the most significant digit is at the head of the list.

For example:
Q1.
int[] nums = {1,2,3,4};
int[] result = plusOne(nums);
the digits are in the result array are {1,2,3,5};

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