2367. 算术三元组的数目

2367. 算术三元组的数目

给你一个下标从 0 开始、严格递增 的整数数组 nums 和一个正整数 diff 。如果满足下述全部条件，则三元组 (i, j, k) 就是一个 算术三元组 ：

• i < j < k ，
• nums[j] - nums[i] == diff 且
• nums[k] - nums[j] == diff

返回不同 算术三元组 的数目。

示例 1：
输入：nums = [0,1,4,6,7,10], diff = 3 输出：2 解释： (1, 2, 4) 是算术三元组：7 - 4 == 3 且 4 - 1 == 3 。 (2, 4, 5) 是算术三元组：10 - 7 == 3 且 7 - 4 == 3 。
示例 2：
输入：nums = [4,5,6,7,8,9], diff = 2 输出：2 解释： (0, 2, 4) 是算术三元组：8 - 6 == 2 且 6 - 4 == 2 。 (1, 3, 5) 是算术三元组：9 - 7 == 2 且 7 - 5 == 2 。

提示：

• 3 <= nums.length <= 200
• 0 <= nums[i] <= 200
• 1 <= diff <= 50
• nums 严格 递增

思路

按题意模拟即可

解答

/**
 * @param {number[]} nums
 * @param {number} diff
 * @return {number}
 */
var arithmeticTriplets = function (nums, diff) {
  const set = new Set();
  let res = 0;
  for (const num of nums) {
    set.add(num);
  }
  for (const num of nums) {
    if (set.has(num + diff) && set.has(num + diff * 2)) res++;
  }
  return res;
};