알고리즘 문제 복습(10~20번)

10번

#include<iostream>
#include<vector>
using namespace std;
int main() {
	int n;
	int cnt=0;
	int temp;
	cin >> n;
	vector<int> arr(n);
	for (int i = 1; i <= n; i++)
	{
		temp = i;
		while (temp!=0)
		{
			temp = temp / 10;
			cnt++;
		}
	}
	cout << cnt;
}

 

11번(중요)

#include<iostream>
#include<vector>
using namespace std;
int main() {
	int c = 1;
	int d = 9;
	int res = 0;
	int sum = 0;
	int n = 0;
	cin >> n;
	while (sum+d<n)
	{
		res = res + (c*d);
		sum = sum + d;
		c++;
		d = d * 10;
	}
	res = res + ((n - sum)*c);
	cout << res;
}

 

12번

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

int main()
{
	char number[9] = {'1','2','3','4','5','6','7','8','9'};
	char arr[100];
	int result[10] = {0};
	int max=0;
	int temp = 0;
	cin >> arr;

	for (int i=0; i < 100; i++)
	{
		for (int j = 0; j < 9; j++)
		{
			if (arr[i] == number[j])
			{
				result[j + 1]++;
			}
		}
	}
	for (int i = 1; i <= 9;i++)
	{
		if (result[i] > max)
		{
			max = result[i];
			temp = i;
		}
		else if (result[i] == max)
		{
			if (temp < i)
			{
				temp = i;
			}
		}
	}
	cout << temp;

}