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package g2301_2400.s2367_number_of_arithmetic_triplets;

// #Easy #Array #Hash_Table #Two_Pointers #Enumeration
// #2022_08_14_Time_3_ms_(66.67%)_Space_42.1_MB_(25.00%)

import java.util.HashSet;
import java.util.Set;

/**
 * 2367 - Number of Arithmetic Triplets\.
 *
 * Easy
 *
 * You are given a **0-indexed** , **strictly increasing** integer array `nums` and a positive integer `diff`. A triplet `(i, j, k)` is an **arithmetic triplet** if the following conditions are met:
 *
 * *   `i < j < k`,
 * *   `nums[j] - nums[i] == diff`, and
 * *   `nums[k] - nums[j] == diff`.
 *
 * Return _the number of unique **arithmetic triplets**._
 *
 * **Example 1:**
 *
 * **Input:** nums = [0,1,4,6,7,10], diff = 3
 *
 * **Output:** 2
 *
 * **Explanation:** 
 *
 * (1, 2, 4) is an arithmetic triplet because both 7 - 4 == 3 and 4 - 1 == 3. 
 *
 * (2, 4, 5) is an arithmetic triplet because both 10 - 7 == 3 and 7 - 4 == 3.
 *
 * **Example 2:**
 *
 * **Input:** nums = [4,5,6,7,8,9], diff = 2
 *
 * **Output:** 2
 *
 * **Explanation:** 
 *
 * (0, 2, 4) is an arithmetic triplet because both 8 - 6 == 2 and 6 - 4 == 2. 
 *
 * (1, 3, 5) is an arithmetic triplet because both 9 - 7 == 2 and 7 - 5 == 2.
 *
 * **Constraints:**
 *
 * *   `3 <= nums.length <= 200`
 * *   `0 <= nums[i] <= 200`
 * *   `1 <= diff <= 50`
 * *   `nums` is **strictly** increasing.
**/
public class Solution {
    public int arithmeticTriplets(int[] nums, int diff) {
        Set set = new HashSet<>();
        for (int x : nums) {
            set.add(x);
        }
        int ans = 0;
        for (int x : nums) {
            if (set.contains(x - diff) && set.contains(x + diff)) {
                ans++;
            }
        }
        return ans;
    }
}