Kolmijako

input/code.cpp: In function 'int main(int, char**)':
input/code.cpp:46:9: warning: unused variable 'a1' [-Wunused-variable]
     int a1 = a2 - 1;
         ^~

#include<bits/stdc++.h>

using namespace std;

int r[101] = {0};


bool doTry(int n, int l){
    if(n < 0 || l < 0) return false;
    if(n == 0){
        if(l == 0) return true;
        else return false;
    }
    if(n == 1){
        if(l != 1) return false;
        if(r[n]) return false;
        r[n] = 2;
        //cout << n << endl;
        return true;
    }

    if(!r[n]){
        r[n] = 2;
        if(doTry(min(n-1, l - n), l - n)){
            //cout << n << endl;
            return true;
        }
        r[n] = 0;
    }
    if(doTry(n-1, l)) return true;
    return false;
}

int main(int argc, char *argv[]){
    int n;
    cin >> n;

    int sum = (1+n)*n/2;

    if(sum % 3){
        cout << "IMPOSSIBLE" << endl;
        return 0;
    }

    int a2 = sum / 3;
    int a1 = a2 - 1;
    int a3 = a2 + 1;

    int t = a3;
    int m = n;
    while(t){
        int s = min(m--, t);
        //cout << s << endl;
        r[s] = 3;
        t -= s;
    }

    //cout << endl;

    t = a2;
    m++;

    if(!doTry(m, a2)){
        cout << "IMPOSSIBLE" << endl;
    }

    char ch[3] = "  ";
    for(int i = 1; i <= n; i++){
        int f = r[i];
        if(!f) f = 1;
        f += '0';
        ch[0] = f;
        cout << ch;
    }

    cout << endl;

    
}

Test 1

Group: 1, 2

Verdict: ACCEPTED

Test 2

Group: 1, 2

Verdict: ACCEPTED

Test 3

Group: 1, 2

Verdict: ACCEPTED

Test 4

Group: 1, 2

Verdict: ACCEPTED

Test 5

Group: 1, 2

Verdict: ACCEPTED

Test 6

Group: 1, 2

Verdict: ACCEPTED

Test 7

Group: 1, 2

Verdict: ACCEPTED

Test 8

Group: 1, 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED

Test 15

Group: 2

Verdict: ACCEPTED