HackerEarth String Restoration problem solution

#include<bits/stdc++.h>
#define LL long long int
#define M 1000000007
#define endl "n"
#define eps 0.00000001
LL pow(LL a,LL b,LL m){ a%=m;LL x=1,y=a;while(b > 0){if(b%2 == 1){x=(x*y);if(x>m) x%=m;}y = (y*y);if(y>m) y%=m;b /= 2;}return x%m;}
LL gcd(LL a,LL b){if(b==0) return a; else return gcd(b,a%b);}
LL gen(LL start,LL end){LL diff = end-start;LL temp = rand()%start;return temp+diff;}
using namespace std;
int p[10001];
int main()  {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t;
    cin >> t;
    while(t--) {
        int n;
        cin >> n;
        int cur = 0;
        char temp = 'a';
        --temp;
        string ans;
        bool flag = 1;
        for(int i = 1; i <= n; i++) {
            cin >> p[i];
            if(p[i] == 0)
                flag = 0;
            if(p[i] != p[i - 1]) {
                ++cur;
                if(cur > 26) {
                    flag = 0;
                }
                else {
                    ++temp;
                }
            }
            if(flag == 1 && cur != p[i]) {
                flag = 0;
            }
            else {
                ans.push_back(temp);
            }
        }
        if(flag) {
            cout << ans << endl;
        }
        else {
            cout << -1 << endl;
        }
    }    
}