Python3 Program to Count triplets with sum smaller than a given value

# A Simple Python 3 program to count triplets with sum smaller
# than a given value

def countTriplets(arr, n, sum):

    # Initialize result
    ans = 0

    # Fix the first element as A[i]
    for i in range( 0 ,n-2):
    
        # Fix the second element as A[j]
        for j in range( i+1 ,n-1):
    
            # Now look for the third number
            for k in range( j+1, n):
                if (arr[i] + arr[j] + arr[k] < sum):
                    ans+=1
    
    return ans

# Driver program
arr = [5, 1, 3, 4, 7]
n = len(arr)
sum = 12
print(countTriplets(arr, n, sum))

#Contributed by Smitha

# Python3 program to count triplets with 
# sum smaller than a given value 


# Function to count triplets with sum smaller
# than a given value         
def countTriplets(arr,n,sum):
    
    # Sort input array
    arr.sort()
    
    # Initialize result 
    ans = 0
    
    # Every iteration of loop counts triplet with 
    # first element as arr[i].
    for i in range(0,n-2):
        
        # Initialize other two elements as corner elements 
        # of subarray arr[j+1..k] 
        j = i + 1
        k = n-1

        # Use Meet in the Middle concept 
        while(j < k):
            
            # If sum of current triplet is more or equal, 
            # move right corner to look for smaller values
            if (arr[i]+arr[j]+arr[k] >=sum):
                k = k-1
            
            # Else move left corner 
            else:
                
                # This is important. For current i and j, there 
                # can be total k-j third elements. 
                ans += (k - j)
                j = j+1
    
    return ans

# Driver program 
if __name__=='__main__':
    arr = [5, 1, 3, 4, 7] 
    n = len(arr) 
    sum = 12
    print(countTriplets(arr, n, sum)) 
    
# This code is contributed by 
# Yatin Gupta