题解 | 自守数

#include <iostream>
#include <cmath>
using namespace std;

static bool isAutomorphicNumber(int num) {
    int squre = num * num;
    int count = 0; // 记录num的位数
    int tmp = num;
    while (tmp > 0) {
        tmp /= 10;
        count++;
    }
    int lastNum = squre % (int)pow(10, count);
    return lastNum == num;
}

int main() {

    int n;
    while (cin >> n) {
        int sum = 0;
        for (int i = 0; i <= n; i++) {
            if (isAutomorphicNumber(i)) {
                sum++;
            }
        }
        cout << sum << endl;
    }

    return 0;
}