Java - 数字中至少有一个7和一个9的数字 [英] Java - numbers with at least one 7 and one 9 in its digit

问题描述

我必须编写一个程序，通过检查每个数字中从1到999,999（强力方法）的数字来确定1,000,000下的正整数有多少至少有一个7和至少一个9。答案应该是199,262。请帮忙！

I have to code a program to determine how many positive integers under 1,000,000 have at least one 7 and at least one 9 among its digits by examining the digits in each number from 1 to 999,999 ("brute-force" method). The answer is supposed to be 199,262. Please help!

推荐答案

如果数字包含7 和 9，那么如何将数字转换为字符串和文本

How about converting the number to a String and text if it contains 7 and 9

    int count = 0;
    for (int i = 1; i < 1000000; i++) {

        String text = String.valueOf(i);
        // contains both
        if (text.contains("7") && text.contains("9")) count++;
    }
    System.out.println(count);

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