Python/backtracking/sum_of_subsets.py
2019-10-05 10:14:13 +05:00

56 lines
1.6 KiB
Python

"""
The sum-of-subsetsproblem states that a set of non-negative integers, and a value M,
determine all possible subsets of the given set whose summation sum equal to given M.
Summation of the chosen numbers must be equal to given number M and one number can
be used only once.
"""
def generate_sum_of_subsets_soln(nums, max_sum):
result = []
path = []
num_index = 0
remaining_nums_sum = sum(nums)
create_state_space_tree(nums, max_sum, num_index, path, result, remaining_nums_sum)
return result
def create_state_space_tree(nums, max_sum, num_index, path, result, remaining_nums_sum):
"""
Creates a state space tree to iterate through each branch using DFS.
It terminates the branching of a node when any of the two conditions
given below satisfy.
This algorithm follows depth-fist-search and backtracks when the node is not branchable.
"""
if sum(path) > max_sum or (remaining_nums_sum + sum(path)) < max_sum:
return
if sum(path) == max_sum:
result.append(path)
return
for num_index in range(num_index, len(nums)):
create_state_space_tree(
nums,
max_sum,
num_index + 1,
path + [nums[num_index]],
result,
remaining_nums_sum - nums[num_index],
)
"""
remove the comment to take an input from the user
print("Enter the elements")
nums = list(map(int, input().split()))
print("Enter max_sum sum")
max_sum = int(input())
"""
nums = [3, 34, 4, 12, 5, 2]
max_sum = 9
result = generate_sum_of_subsets_soln(nums, max_sum)
print(*result)