"greatest product given 'n' adjacent digits" 的计算行为不一致（D 语言）

Question

我正在为 Project Euler (problem 8) 制定解决方案，其中涉及计算 13 个相邻数字的最大乘积。我写了一个解决方案（如下）但是当切片的长度为 13 时它似乎没有输出正确的答案。当我将相邻数字的长度设置为“4”而不是“13”时它是正确的。你能帮我找出错误吗？

这是写在 D programming language:

/*
 * Project Euler: Classic, "Largest product in a series" solution
 * Implementation by A. S. "Aleksey" Ahmann <hackermaneia@riseup.net>
 * - https://github.com/Alekseyyy
 *
 * Problem link: https://projecteuler.net/problem=8
 */

import std.stdio : writeln;
import std.array : replace;
import std.conv : to;

string number = "73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450";

void main() {

    number = replace(number, "\n", "");
    int[] x = format_adjacent(number);
    int largest_product = largestProduct(x, 13);

    writeln(largest_product);
}

int[] format_adjacent(string number) {

    int[] adjacent_numbers;
    for (int i = 0; i < number.length; i++)
        adjacent_numbers ~= to!int(number[i] - to!char("0"));
    return adjacent_numbers;
}

int computeProduct(int[] sequence) {

    int product = sequence[0];
    for (int i = 1; i < sequence.length; i++)
        product = product * sequence[i];
    return product;
}

int largestProduct(int[] sequence, int slice) {

    int largest_product = 0;

    int n = 0;
    int fin = to!int(sequence.length) - (slice - 1);

    while (n < fin) {
        int[] seq = sequence[n .. n + slice];
        int product = computeProduct(seq);
        if (product > largest_product)
            largest_product = product;
        n = n + 1;
    }
    return largest_product;
}

Answer 1

int有多大？我尝试在 C 中使用 64 位整数为计算的产品编写这样的程序，发现最大的 13 个字符来自字符串 5576689664895（字符串第 4 行末尾有 557）并且产品是，十六进制 0x57994b000 不适合 32 位。

Answer 2

int computeProduct(int[] sequence) {
    import std.experimental.checkedint;


    int product = sequence[0];
    for (int i = 1; i < sequence.length; i++)
        product = (checked(product) * sequence[i]).get;
    return product;
}

仅对您的程序进行此修改（导入，围绕一个变量检查（n），然后 .get 返回一个 int），您会遇到运行时错误（即使使用 -O，即使使用 -release） :

Overflow on binary operator: int(371589120) * const(int)(8)

具有此更改的程序的 long 版本为您提供了正确的答案，没有溢出，运行时成本小到我无法衡量它。

"greatest product given 'n' adjacent digits" 的计算行为不一致（D 语言）

Inconsitent behaviour with computation of "greatest product given 'n' adjacent digits" (D language)

math

slice

d

multiplication

voting