## 题目

Given an array of n integers nums and a target, find the number of index triplets `i, j, k`

with `0 <= i < j < k < n`

that satisfy the condition `nums[i] + nums[j] + nums[k] < target`

.

**Example:**

Input:nums = [-2,0,1,3], and target = 2Output:2Explanation:Because there are two triplets which sums are less than 2:

[-2,0,1]

[-2,0,3]