数字统计

直接枚举

#include<iostream>
using namespace std;
int l,r;

int count(int n)
{
    int sum = 0;
    while(n)
    {
        if(n%10 == 2)   sum ++;
        n = n/10;
    }
    return sum;
}

int main()
{
    scanf("%d%d",&l,&r);

    int res = 0;
    for(int i = l;i <= r;i ++)   res += count(i);

    printf("%d",res);
}