62 lines
1.6 KiB
Python
62 lines
1.6 KiB
Python
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def generate_triangle():
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t = 0
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ts = [[]]
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i_in_row, max_in_row = 0, 1
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for _ in range(1, 500_500 + 1):
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t = (615_949 * t + 797_807) % 2**20
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s = t - 2**19
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ts[-1].append(s)
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i_in_row += 1
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if i_in_row == max_in_row:
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i_in_row = 0
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max_in_row += 1
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ts.append([])
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ts.pop() # remove empty list
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return ts
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def array_to_prefix_sum_array(xs):
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ys = []
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current_sum = 0
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for x in xs:
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current_sum += x
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ys.append(current_sum)
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return ys
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def range_sum(prefix_sum, i, j):
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if i == 0:
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return prefix_sum[j]
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else:
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return prefix_sum[j] - prefix_sum[i - 1]
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def find_min_triangle(row_i, col_i, sum_triangle):
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current_sum, min_sum = 0, float("inf")
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left_i, right_i = col_i, col_i
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while row_i < len(sum_triangle):
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current_sum += range_sum(sum_triangle[row_i], left_i, right_i)
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row_i += 1
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right_i += 1
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min_sum = min(current_sum, min_sum)
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return min_sum
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def euler_150():
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triangle = generate_triangle()
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# triangle = [[15], [-14, -7], [20, -13, -5], [-3, 8, 23, -26], [1, -4 , -5, -18, 5], [-16, 31, 2, 9, 28, 3]]
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sum_triangle = [array_to_prefix_sum_array(xs) for xs in triangle]
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min_triangle = float("inf")
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for row_i in range(len(triangle)):
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for col_i in range(len(triangle[row_i])):
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potential_min = find_min_triangle(row_i, col_i, sum_triangle)
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min_triangle = min(min_triangle, potential_min)
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return min_triangle
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if __name__ == "__main__":
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solution = euler_150()
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print("e150.py: " + str(solution))
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assert solution == -271248680
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