ABC114-C 755

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("575");
            //4
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("3600");
            //13
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("999999999");
            //26484
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        int[] wkArr = InputList[0].Split(' ').Select(X => int.Parse(X)).ToArray();
        int N = wkArr[0];

        string[] wk753Arr = Derive753Arr();

        int Answer = 0;
        foreach (string EachStr in wk753Arr) {
            if (int.Parse(EachStr) <= N) {
                Answer++;
            }
        }
        Console.WriteLine(Answer);
    }

    static string[] Derive753Arr()
    {
        var WillReturn = new List<string>();

        var Stk = new Stack<string>();
        Stk.Push("");

        while (Stk.Count > 0) {
            string Popped = Stk.Pop();
            if (Popped.Contains("3") && Popped.Contains("5") && Popped.Contains("7")) {
                WillReturn.Add(Popped);
            }
            if (Popped.Length == 9) {
                continue;
            }

            Stk.Push(Popped + "3");
            Stk.Push(Popped + "5");
            Stk.Push(Popped + "7");
        }
        return WillReturn.ToArray();
    }
}

解説

深さ優先探索を使ってます。