diff --git a/project_euler/problem_142/__init__.py b/project_euler/problem_142/__init__.py new file mode 100644 index 000000000000..e69de29bb2d1 diff --git a/project_euler/problem_142/sol1.py b/project_euler/problem_142/sol1.py new file mode 100644 index 000000000000..0b1b49b27ef7 --- /dev/null +++ b/project_euler/problem_142/sol1.py @@ -0,0 +1,80 @@ +""" +Project Euler Problem 142: https://projecteuler.net/problem=142 + +Perfect Square Collection + +Find the smallest x + y + z with integers x > y > z > 0 such that +x + y, x - y, x + z, x - z, y + z, y - z are all perfect squares. + + +Change the variables to a, b, c, so that 3 requirements are satisfied automatically: +a^2 = y - z +b^2 = x - y +c^2 = z + x + +and the rest of requirements for perfect squares are: +z + y = c^2 - b^2 +y + x = a^2 + c^2 +x - z = a^2 + b^2 + +Then iterate over a^2, b^2 and c^2 to check if the combination satisfies all +3 requirements. + +The total sum x + y + z = (a^2 - b^2 + 3c^2) / 2, so we break loop for c^2 if +the sum is already bigger than found sum. + +""" + + +def solution(number_of_terms: int = 3) -> int | None: + """ + + Iterate over combinations of a, b, c and save min sum. + In case only one term x = 1 is solution. + In case of two terms, x = 5, y = 4 is the solution. + + >>> solution(1) + 1 + >>> solution(2) + 9 + """ + + if number_of_terms == 1: + return 1 + if number_of_terms == 2: + return 9 + + n_max = 2500 + squares: list[int] = [] + + for a in range(n_max + 1): + squares += [a * a] + squares_set = set(squares) + + min_sum = None + for a in range(1, len(squares)): + a_sq = squares[a] + for b in range(1, len(squares)): + b_sq = squares[b] + if a_sq + b_sq not in squares_set: + continue + for c in range(max(a, b) + 1, len(squares)): + c_sq = squares[c] + # break if x + y + z is already bigger than min_sum: + if min_sum is not None and (a_sq - b_sq + 3 * c_sq) // 2 > min_sum: + break + if (c_sq - b_sq in squares_set) and (a_sq + c_sq in squares_set): + x2, y2, z2 = ( + a_sq + b_sq + c_sq, + a_sq - b_sq + c_sq, + c_sq - a_sq - b_sq, + ) + if z2 > 0 and x2 % 2 == 0 and y2 % 2 == 0 and z2 % 2 == 0: + sum_ = (x2 + y2 + z2) // 2 + min_sum = sum_ if min_sum is None else min(min_sum, sum_) + + return min_sum + + +if __name__ == "__main__": + print(f"{solution() = }")