例如
i=1;
to_string(i)=”1”

https://codeforces.com/contest/1560/problem/D

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const ll P2LIM = (ll)2e18;
vector<string> ts;
int solve(string s, string t)
{
    int tp = 0;
    int sp = 0;
    int taken = 0;

    while (sp < s.length() && tp < t.length())
    {
        if(s[sp] == t[tp])
        {
            taken++;
            tp++;
        }
        sp++;
    }

    return (int)s.length() - taken + (int)t.length() - taken;
}
int main()
{
    for (ll p2 = 1; p2 <= P2LIM; p2 *= 2)
        ts.push_back(to_string(p2));

    int t;
    cin >> t;

    while (t--)
    {
        string n;
        cin >> n;

        int ans = n.length() + 1;
        for (auto p2 : ts)
            ans = min(ans, solve(n, p2));
        cout << ans << '\n';
    }

    return 0;
}

https://www.acwing.com/activity/content/code/content/1730529/

#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

int main()
{
    int T;
    cin >> T;
    while (T -- )
    {
        string str;
        cin >> str;
        int n = str.size();

        int res = 100;
        for (int i = 0; i < 1 << n; i ++ )
        {
            int x = 0;
            for (int j = 0; j < n; j ++ )
                if (i >> j & 1)
                    x = x * 10 + str[j] - '0';

            int t = sqrt(x);
            if (x && t * t == x) res = min(res, n - (int)to_string(x).size());
        }
        if (res == 100) res = -1;
        cout << res << endl;
    }

    return 0;
}