codeforces 110A（Nearly Lucky Number） Java_codeforce 110a nearly lucky number

加班回到寝室，再来刷一波水题！！！

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * 题意：如果一个数中 4和7 的个数为lucky number（每位数字仅仅是 4或7），则该数是nearly lucky number，问该数是不是nearly lucky number？
 *
 * @author TinyDolphin
 *         2017/6/26 22:15.
 */
public class Main {

    /**
     * 判断该数是否是幸运数字（即仅仅包含4和7）
     */
    public static boolean isLuckNum(int num) {
        String str = num + "";
        for (int index = 0; index < str.length(); index++) {
            if (str.charAt(index) != '4' && str.charAt(index) != '7') {
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) throws IOException {
        //StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
        String inputNum;     // 输入的数
        int luckPosition;   // 记录幸运位
        while (in.hasNext()) {
            inputNum = in.next();
            luckPosition = 0;
            char temp;
            for (int index = 0; index < inputNum.length(); index++) {
                temp = inputNum.charAt(index);
                if (temp == '4' || temp == '7') {
                    luckPosition++;
                }
            }
            out.println(isLuckNum(luckPosition) ? "YES" : "NO");
        }
        out.flush();
    }
}
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