Formatted question description: https://leetcode.ca/all/1534.html

1534. Count Good Triplets (Easy)

Given an array of integers arr, and three integers ab and c. You need to find the number of good triplets.

A triplet (arr[i], arr[j], arr[k]) is good if the following conditions are true:

  • 0 <= i < j < k < arr.length
  • |arr[i] - arr[j]| <= a
  • |arr[j] - arr[k]| <= b
  • |arr[i] - arr[k]| <= c

Where |x| denotes the absolute value of x.

Return the number of good triplets.

 

Example 1:

Input: arr = [3,0,1,1,9,7], a = 7, b = 2, c = 3
Output: 4
Explanation: There are 4 good triplets: [(3,0,1), (3,0,1), (3,1,1), (0,1,1)].

Example 2:

Input: arr = [1,1,2,2,3], a = 0, b = 0, c = 1
Output: 0
Explanation: No triplet satisfies all conditions.

 

Constraints:

  • 3 <= arr.length <= 100
  • 0 <= arr[i] <= 1000
  • 0 <= a, b, c <= 1000

Related Topics:
Array

Solution 1. Brute force

// OJ: https://leetcode.com/problems/count-good-triplets/

// Time: O(N^3)
// Space: O(1)
class Solution {
public:
    int countGoodTriplets(vector<int>& A, int a, int b, int c) {
        int N = A.size(), ans = 0;
        for (int i = 0; i < N; ++i) {
            for (int j = i + 1; j < N; ++j) {
                for (int k = j + 1; k < N; ++k) {
                    if (abs(A[i] - A[j]) <= a && abs(A[j] - A[k]) <= b && abs(A[i] - A[k]) <= c) ++ans;
                }
            }
        }
        return ans;
    }
};

Java

class Solution {
    public int countGoodTriplets(int[] arr, int a, int b, int c) {
        int triplets = 0;
        int length = arr.length;
        for (int i = 0; i < length; i++) {
            int num1 = arr[i];
            for (int j = i + 1; j < length; j++) {
                int num2 = arr[j];
                if (Math.abs(num1 - num2) > a)
                    continue;
                for (int k = j + 1; k < length; k++) {
                    int num3 = arr[k];
                    if (Math.abs(num2 - num3) <= b && Math.abs(num1 - num3) <= c)
                        triplets++;
                }
            }
        }
        return triplets;
    }
}

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