Code Log - Day 14

Log

Today i finished a LeetCode problem from the Top 150 Interview Questions list and an assignment from my university.

LeetCode

The LeetCode exercise i chose was: Rotate Array. It requires a function that receive as input an integer array and their k number of rotations to the right  rotate the array to the right by k steps :

Given an integer array nums, rotate the array to the right by k steps, where k is non-negative. Could you do it in-place with O(1) extra space?

My approach was to subtract k from the array length and use the result as the number of digits in the end of the array that would be swapped with the k first ones, and, then, i would "sort" the ones in the beginning that now are at the end of the array. However, this solution didn't work for some test cases, due to the subtraction of k from the array length (when k > length). An alternative, that works well and can be found here, rotates de array by reversing all item and using a new k value given by k % nums.length as a index to reverse the values before the new k and then then values after the new k:

class Solution {
    public void rotate(int[] nums, int k) {
        // ex.: nums = [1,2,3,4,5,6,7], k = 11
        k %= nums.length; // k = 11 % 7 = 4

        reverse(nums, 0, nums.length - 1); // [1,2,3,4,5,6,7] -> [7,6,5,4,3,2,1]
        reverse(nums, 0, k - 1); // [7,6,5,4,3,2,1] -> [4,5,6,7,3,2,1]
        reverse(nums, k, nums.length - 1); // [4,5,6,7,3,2,1] -> [4,5,6,7,1,2,3]
    }

    private void reverse(int[] nums, int left, int right) {
        while (left < right) {
            int temp = nums[left];
            nums[left] = nums[right];
            nums[right] = temp;
            left++;
            right--;
        }
    }
}

Assignments

The assignment was from the Distributed System class and it required to build a chat app using MQTTv5. It basically needed to send messages to an specified "topic" or subscribe to one. For this, the Eclipse Paho provides a publish and subscribe methods, so most part of the work was on the input string parsing.