Citadel Hackerrank

# 1. Find all triplets d[a] < d[b] < d[c] where d[a] + d[b] + d[c] <= t.
from bisect import bisect_right
 
def function(d, t):
	N = len(d)
	res = 0
	for i in range(1, N):
		prev = d[i - 1]
 
		left = i
		right = N - 1
 
		while left < right:
			total = prev + d[left] + d[right]
 
			if total <= t:
				res += right - left
				left += 1
			else:
				target = t - prev - d[left]
				right = bisect_right(d, target) - 1
	return res

# 2. Inversions of length 3 -> # of decreasing subsequences of length 3 in arr
def function(arr):
	N = len(arr)
	dp = [0] * N
	for i in range(N):
		for j in range(i + 1, N):
		dp[i] = int(arr[i] > arr[j])
 
	return sum(dp[j] for i in range(N) for j in range(i + 1, N) if arr[i] > arr[j])