ABC406-B Product Calculator

問題へのリンク

C#のソース

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("5 2");
            WillReturn.Add("7 13 3 2 5");
            //10
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("2 1");
            WillReturn.Add("2 5");
            //1
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        decimal[] wkArr = InputList[0].Split(' ').Select(pX => decimal.Parse(pX)).ToArray();
        decimal K = wkArr[1];

        decimal[] AArr = InputList[1].Split(' ').Select(pX => decimal.Parse(pX)).ToArray();

        decimal Limit = 1;
        for (int I = 1; I <= K; I++) {
            Limit *= 10;
        }
        Limit--;

        decimal CurrVal = 1;
        foreach (decimal EachA in AArr) {
            if (WillOverProd(CurrVal, EachA, Limit)) {
                CurrVal = 1;
            }
            else {
                CurrVal *= EachA;
            }
        }
        Console.WriteLine(CurrVal);
    }

    // decimal型の2正数の掛け算が、Limitを超えるかを返す
    static bool WillOverProd(decimal pA, decimal pB, decimal pLimit)
    {
        decimal Mod = pLimit % pB;
        pLimit -= Mod;

        return pA > pLimit / pB;
    }
}

解説

WillOverProdメソッドでオーバフローを事前検知してます。