A_AquaMoon_and_Two_Arrays.cpp

    #include<bits/stdc++.h>

    #define pb push_back
    #define mp make_pair 
    #define fr first
    #define sc second
    #define clr(a) memset(a, 0, sizeof(a))
    #define sz(x) x.size()
    #define rep(n) for (ll i = 0; i < n; i++)
    #define repc(i, n) for (ll i = 0; i < n; i++)
    #define FOR(i, x, y) for (int i = x; i < y; i++)
    #define DEC(i, x, y) for (int i = x; i >= y; i--)
    #define all(v) v.begin(), v.end()
    #define min3(a, b, c) min(a, min(b, c))
    #define max3(a, b, c) max(a, max(b, c))
    #define alla(a, n) a, a + n

    using namespace std;

    // Some typedef's
    typedef long long ll;
    typedef unsigned long long ull;
    typedef pair<ll, ll> ii;
    typedef vector<ll> vi;
    typedef vector<ii> vii;

    // Some frequently used functions
    template <typename T>
    T modpow(T base, T exp, T modulus){  
        base %= modulus;  T result = 1;  
        while(exp > 0){    
            if(exp & 1) result = (result * base) % modulus;    
            base = (base * base) % modulus;    
            exp >>= 1;  
        }  
        return result;
    }
    ll lcm(ll a, ll b) { return (a * (b / __gcd(a, b))); }
    //Repeat,Example,Approach,Code,Testcases,Optimize
    // int overflow, array bounds special cases (n=1?) 
    // do smth instead of nothing and stay organized 
    // WRITE STUFF DOWN DON'T GET STUCK ON ONE APPROACH

    // Some contants
    const int inf = 1e9 + 7;
    const double eps = 1e-6;
    const double pi = 1.00 * acos(-1.00);



    void solve(){
        int n;
        cin >> n;
        int x;
        vector<int>v,vx;
        vector<pair<int,int>>vec;
        for(int i = 0; i < n; i++){
            cin >> x;
            v.pb(x);
        }    
        for(int i = 0; i < n; i++){
            cin >> x;
            vx.pb(x);
        }
        for(int i = 0; i < n; i++){
            if(v[i] == vx[i]){
                continue;
            }
            else if(v[i] > vx[i]){
                int j = i+1;
                while(v[i] > vx[i]){
                    if(j == n){
                        cout << -1 << endl;
                        return;
                    }
                    if(v[j] == vx[j] || v[j] > vx[j]){
                        j++;
                    }
                    else if(v[j] < vx[j]){
                        v[i]--;
                        v[j]++;
                        vec.push_back({i+1,j+1});
                    }
                }
            }
            else if(v[i] < vx[i]){
                int j = i+1;
                while(v[i] < vx[i]){
                    if(j == n){
                        cout << -1 << endl;
                        return;
                    }
                    if(v[j] == vx[j] || v[j] < vx[j]){
                        j++;
                    }
                    else if(v[j] > vx[j]){
                        v[j]--;
                        v[i]++;
                        vec.push_back({j+1,i+1});
                    }
                }
            }
        }
        cout << vec.size() << endl;
        for(auto i:vec){
            cout << i.first << " " << i.second << endl;
        }
    }

    int main(){
        ios_base::sync_with_stdio(false); cin.tie(NULL);cout.tie(NULL) ;
        int t;
        cin >> t;
        while(t--){
            solve();
        }
    }