Given a list of integers, write a Python program to find all triplets that sum up to given integer ‘k’.
Examples:
Input : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], k = 10 Output : [(1, 5, 4), (1, 6, 3), (1, 7, 2), (2, 5, 3)] Input : [12, 3, 6, 1, 6, 9], k = 24 Output : [(12, 6, 6), (12, 9, 3)]
Approach #1 : Naive (Using set)
In this approach, we use two for loops. The first loop sets first element, another to check whether other two elements including first sums up to k or not. This approach takes O(n2) time complexity.
# Python3 program to Find total number # of triplets in a temp_list with given k def findTriplets(lst, k): triplet_count = 0 final_temp_list = [] for i in range ( 0 , len (lst) - 1 ): s = set () temp_list = [] # Adding first element temp_list.append(lst[i]) curr_k = k - lst[i] for j in range (i + 1 , len (lst)): if (curr_k - lst[j]) in s: triplet_count + = 1 # Adding second element temp_list.append(lst[j]) # Adding third element temp_list.append(curr_k - lst[j]) # Appending tuple to the final list final_temp_list.append( tuple (temp_list)) temp_list.pop( 2 ) temp_list.pop( 1 ) s.add(lst[j]) return final_temp_list # Driver Code lst = [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ] k = 10 print (findTriplets(lst, k)) |
[(1, 5, 4), (1, 6, 3), (1, 7, 2), (2, 5, 3)]
Approach #2 : Using itertools
Python itertools module provide combination(iterable, r) function. This tool returns the r length subsequences of elements from the input iterable. Every time we make a combination of 3 elements and check if they sums up to k or not.
# Python3 program to Find total number # of triplets in a list with given sum from itertools import combinations def findTriplets(lst, key): def valid(val): return sum (val) = = key return list ( filter (valid, list (combinations(lst, 3 )))) # Driver Code lst = [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ] print (findTriplets(lst, 10 )) |
[(1, 2, 7), (1, 3, 6), (1, 4, 5), (2, 3, 5)]
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