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# Program to check number of triplets from an array whose sum is less than target or not Python

Suppose we have a list of numbers called nums and another value target, we have to find the number of triples (i < j < k) that exist such that nums[i] + nums[j] + nums[k] < target.

So, if the input is like nums = [−2, 6, 4, 3, 8], target = 12, then the output will be 5, as the triplets are: [−2,6,4], [−2,6,3], [−2,4,3], [−2,4,8], [−2,3,8]

To solve this, we will follow these steps −

sort the list nums

ans := 0

n := size of nums

for i in range 0 to n−1, do

k := n − 1

for j in range i + 1 to n−1, do

while k > j and nums[i] + nums[k] + nums[j] >= target, do

k := k − 1

if j is same as k, then

ans := ans + k − j

return ans

Let us see the following implementation to get better understanding −

## Example

class Solution: def solve(self, nums, target): nums.sort() ans = 0 n = len(nums) for i in range(n): k = n − 1 for j in range(i + 1, n): while k > j and nums[i] + nums[k] + nums[j] >= target: k -= 1 if j == k: break ans += k − j return ans ob1 = Solution() nums = [−2, 6, 4, 3, 8] target = 12 print(ob1.solve(nums, target))

## Input

[-2, 6, 4, 3, 8], 12

## Output

5

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