Today I have done Number of Boomerangs and leetcode's April LeetCoding Challenge with cpp.

Number of Boomerangs

Description

You are given n points in the plane that are all distinct, where points[i] = [xi, yi]. A boomerang is a tuple of points (i, j, k) such that the distance between i and j equals the distance between i and k (the order of the tuple matters).

Return the number of boomerangs.

Example 1:

Input: points = [[0,0],[1,0],[2,0]]
Output: 2
Explanation: The two boomerangs are [[1,0],[0,0],[2,0]] and [[1,0],[2,0],[0,0]].

Example 2:

Input: points = [[1,1],[2,2],[3,3]]
Output: 2

Example 3:

Input: points = [[1,1]]
Output: 0

Constraints:

• n == points.length
• 1 <= n <= 500
• points[i].length == 2
• -104 <= xi, yi <= 104
• All the points are unique.

Solution

constexpr int distance(int x1, int y1, int x2, int y2) {
  return (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
}

class Solution {
public:
  int numberOfBoomerangs(vector<vector<int>>& points) {
    int len = points.size();
    int answer = 0;
    for(auto &p : points) {
      unordered_map<int, int> cnt;
      for(auto &pp : points) {
        int d = distance(p[0], p[1], pp[0], pp[1]);
        answer += 2 * cnt[d];
        cnt[d] += 1;
      }
    }
    return answer;
  }
};

April LeetCoding challenge 7

Description

Determine if String Halves Are Alike

You are given a string s of even length. Split this string into two halves of equal lengths, and let a be the first half and b be the second half.

Two strings are alike if they have the same number of vowels ('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'). Notice that s contains uppercase and lowercase letters.

Return true if a and b are alike. Otherwise, return false.

Example 1:

Input: s = "book"
Output: true
Explanation: a = "bo" and b = "ok". a has 1 vowel and b has 1 vowel. Therefore, they are alike.

Example 2:

Input: s = "textbook"
Output: false
Explanation: a = "text" and b = "book". a has 1 vowel whereas b has 2. Therefore, they are not alike.
Notice that the vowel o is counted twice.

Example 3:

Input: s = "MerryChristmas"
Output: false

Example 4:

Input: s = "AbCdEfGh"
Output: true

Constraints:

• 2 <= s.length <= 1000
• s.length is even.
• s consists of uppercase and lowercase letters.

Solution

constexpr int vowel(char c) {
  switch(c) {
    case 'a':
    case 'e':
    case 'i':
    case 'o':
    case 'u':
    case 'A':
    case 'E':
    case 'I':
    case 'O':
    case 'U':
      return 1;
  }
  return 0;
}
class Solution {
public:
  bool halvesAreAlike(string s) {
    int front = 0;
    int back = 0;
    int len = s.length();
    for(int i = 0; i < len / 2; ++i) {
      front += vowel(s[i]);
    }
    for(int i = len / 2; i < len; ++i) {
      back += vowel(s[i]);
    }
    return front == back;
  }
};