题解 | #自守数#

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

int judg(int n){
    char str[100001];
    sprintf(str, "%d", n);
    int len = strlen(str);
    
    int squ = pow(n, 2);
    int tmp = squ % (int)pow(10, len);  

    if(tmp == n)
        return 1;
    else
        return 0;
}

int main(){

    int n;
    scanf("%d", &n);
    
    int count = 0;
    for(int i = 0; i <= n; i++){
        while(judg(i)){
            count++;
            break;
        }
    }

    printf("%d", count);

    return 0;
}