暴力枚举

import java.util.Random;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int num = sc.nextInt();
            int ans;
            String str = Integer.toString(num);
            int x = (int)(Math.sqrt(num));
            if(num == 1) System.out.println(1);
            else {
                if(x * x == num){
                    System.out.println(0);
                }else {
                    boolean flag = true;
                    while (x > 0){
                        int l = 0;//双指针
                        int r = 0;
                        flag = true;
                        String a1 = Integer.toString(--x * x);
                        while(r < a1.length()){
                            if(l >= str.length()){
                                flag = false;
                                break;
                            }
                            if(str.charAt(l) == a1.charAt(r)){
                                l++;
                                r++;
                            }else {
                                l++;
                            }
                        }
                        if(flag) {
                            break;
                        }
                    }
                    String s = Integer.toString(x * x);
                    ans = str.length() - s.length();
                    if(flag){
                        if(x == 0) System.out.println(-1);
                        else System.out.println(ans);
                    }
                    else System.out.println(-1);
                }
        }
    }
}

枚举从1到n的平方数

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define endl '\n'
void solve();

int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int t=1;
//	cin>>t;
	while(t--){
		solve();
	}
	return 0;
}

void solve(){
	int n;
	cin>>n;
	string s=to_string(n);
	int ans=-1;
	for(int i=1;i<=n/i;i++){
		int t=i*i;
		stack<char>st;
		while(t){
			st.push(t%10+'0');
			t/=10;
		}
		int l=st.size();
		for(auto c:s){
			if(st.size()&&c==st.top())
				st.pop();
		}
		if(st.empty()){
			ans=max(ans,l);
		}
	}
	if(ans==-1)
		cout<<ans<<endl;
	else
		cout<<s.size()-ans<<endl;
}

二进制枚举，注意开头不能为零

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include<stack>
#include<queue>
using namespace std;
#define int long long
const int MOD= 998244353;
void solve() {
	string s;cin>>s;
    int n=s.length();
    int mx=-1;
    for(int i=(1<<n)-1;i>0;i--){
        int num=0,ans=0;
       for(int j=0;j<n;j++){
        if((i>>(j))&1){
            if(ans==0&&s[j]=='0'){
                break;
            }
            ans++;
            num=num*10+s[j]-'0';
        }
       }
    //    1881388645
       int x=sqrt(num);
       if(x*x==num&&num>0){
        mx=max(mx,ans);
       }
    }
    if(mx==-1){
    cout<<-1<<endl;
    }else{
        cout<<n-mx<<endl;
    }
	return;
}
signed main()
{
    iostream::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    solve();
    // int t;cin>>t;
    // while(t--){
    //     solve();
    // }
    return 0;
}