题解 | #自守数#

#include <stdio.h>
#include <string.h>
#include <math.h>

//自守数  判断是几位  平方后对10的位数次方取余
//87909376  9376 87900000%10000
//pow(),需要加载math.h

int isself(int n);
int main()
{
    int n;
    while (scanf("%d", &n) != EOF)
    {
        int count = 0;
        for (int i = 0; i <= n; i++)
            if (isself(i) == 1)
                count++;

        printf("%d\n", count);
    }

    return 0;
}

int isself(int n)
{
    int ret = 0;
    int digit = 0;
    int cmpn = n * n - n;
    while (n != 0)
    {
        digit++;
        n /= 10;
    }
    int rank = pow(10, digit);

    if (cmpn % rank == 0)
    {
        ret = 1;
    }
    return ret;
}