6136. 算术三元组的数目

题目描述

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。

输入输出

1
2
3
4
5
6
7
8
9
10
11
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 。

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 。

基本思路

三指针法 时复$O(n^2)$ 空复$O(n)$

java实现

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
class Solution {
    public int arithmeticTriplets(int[] nums, int diff) {
        int len = nums.length;
        int res = 0;
        for(int i = 0; i < len; i++){
            int j = i + 1;
            while(j < len && nums[j] - nums[i] < diff){
                j++;
            }
            int k = j + 1;
            while(k < len && nums[k] - nums[j] < diff){
                k++;
            }
            if(k < len && nums[k] - nums[j] == diff && nums[j] - nums[i] == diff){
                res++;
            }
        }
        return res;
    }
}