Today I have done Reverse Subarray To Maximize Array Value and leetcode's March LeetCoding Challenge with cpp.

Reverse Subarray To Maximize Array Value

Description

You are given an integer array nums. The value of this array is defined as the sum of |nums[i]-nums[i+1]| for all 0 <= i < nums.length-1.

You are allowed to select any subarray of the given array and reverse it. You can perform this operation only once.

Find maximum possible value of the final array.

Example 1:

Input: nums = [2,3,1,5,4]
Output: 10
Explanation: By reversing the subarray [3,1,5] the array becomes [2,5,1,3,4] whose value is 10.

Example 2:

Input: nums = [2,4,9,24,2,1,10]
Output: 68

Constraints:

• 1 <= nums.length <= 3*10^4
• -10^5 <= nums[i] <= 10^5

Solution

check O(n) Solution with explanation , very clear explanation with helpful image which helps me a lot.

class Solution {
public:
  int maxValueAfterReverse(vector<int>& nums) {
    int len = nums.size();
    int value = 0;
    for(int i = 1; i < len; ++i) value += abs(nums[i] - nums[i - 1]);
    if(len < 3) return value;
    
    int mmin = INT_MAX;
    int mmax = INT_MIN;
    for(int i = 0; i < len - 1; ++i) {
      mmin = min(mmin, max(nums[i], nums[i + 1]));
      mmax = max(mmax, min(nums[i], nums[i + 1]));
    }
    int change = (mmax - mmin) * 2;
    for(int i = 1; i < len; ++i) {
      int swap = abs(nums[0] - nums[i]) - abs(nums[i] - nums[i - 1]);
      change = max(swap, change);
    }
    for(int i = 0; i < len - 1; ++i) {
      int swap = abs(nums.back() - nums[i]) - abs(nums[i] - nums[i + 1]);
      change = max(swap, change);
    }
    return value + change;
  }
};

March LeetCoding Challenge 17

Description

Generate Random Point in a Circle

Given the radius and x-y positions of the center of a circle, write a function randPoint which generates a uniform random point in the circle.

Note:

1. input and output values are in floating-point.
2. radius and x-y position of the center of the circle is passed into the class constructor.
3. a point on the circumference of the circle is considered to be in the circle.
4. randPoint returns a size 2 array containing x-position and y-position of the random point, in that order.

Example 1:

Input: 
["Solution","randPoint","randPoint","randPoint"]
[[1,0,0],[],[],[]]
Output: [null,[-0.72939,-0.65505],[-0.78502,-0.28626],[-0.83119,-0.19803]]

Example 2:

Input: 
["Solution","randPoint","randPoint","randPoint"]
[[10,5,-7.5],[],[],[]]
Output: [null,[11.52438,-8.33273],[2.46992,-16.21705],[11.13430,-12.42337]]

Explanation of Input Syntax:

The input is two lists: the subroutines called and their arguments. Solution's constructor has three arguments, the radius, x-position of the center, and y-position of the center of the circle. randPoint has no arguments. Arguments are always wrapped with a list, even if there aren't any.

Solution

already done before

const double pi = 3.14159265358979323846264338327950288419;

class Solution {
  random_device rd;
  mt19937 gen;
  uniform_real_distribution<double> distr;
  double r;
  double x;
  double y;
public:
  Solution(double radius, double x_center, double y_center): r(radius), x(x_center), y(y_center) {
    gen = mt19937(rd());
    distr = uniform_real_distribution<double>(0, 1);
  }

  vector<double> randPoint() {
    double r = this->r * sqrt(distr(gen));
    double t = distr(gen) * 2 * pi;
    return {x + r * cos(t), y + r * sin(t)};
  }
};