直接大力出奇迹

/**
 * 雷劈数：两个数和的平方恰好等于这两个数直接拼接起来
 * 举例：(494+209)² = 494209
 * 思路：设上式为(x+y)² = z， z = x * 10^N+y，其中N为y的位数减1。
 */
public class 雷劈数 {
    static final long[] POWERS_OF_10 = {1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000};
    public static void main(String[] args) {
        for (long x = 0; x < 10000; x++) {
            for (long y = 0; y < 10000; y++) {
                long sumPower = (x + y) * (x + y);
                long powerSum = x * (power10(log10(y))) + y;
                if (sumPower == powerSum)
                    System.out.printf("(%d+%d)² = %d\n", x, y, sumPower);
            }
        }
    }
    static long power10(long pow) {
        return POWERS_OF_10[(int) pow];
    }
    static long log10(long num) {
        if (num < 10) return 1;
        if (num < 100) return 2;
        if (num < 1000) return 3;
        if (num < 10000) return 4;
        if (num < 100000) return 5;
        if (num < 1000000) return 6;
        if (num < 10000000) return 7;
        if (num < 100000000) return 8;
        if (num < 1000000000) return 9;
        return 0;
    }
}

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