import sys
input = sys.stdin.readline
inf = float('inf')
def getInt():
return int(input())
def getStr():
return input().strip()
def getList(split=True):
s = getStr()
if split:
s = s.split()
return map(int, s)
t = getInt()
def solve():
n = getInt()
a = list(getList())
b = list(getList())
if sum(a) != sum(b):
print(-1)
else:
res = []
p = []
q = []
for i in range(n):
diff = a[i] - b[i]
if diff < 0 :
q.extend([i+1] * -diff)
elif diff > 0:
p.extend([i+1] * diff )
print(len(p))
for i,j in zip(p, q):
print(i,j)
for _ in range(t):
solve()
#include <bits/stdc++.h>
#define int long long
#define pii pair<int, int>
using namespace std;
const int N = 1e6 + 10;
inline void solve() {
int n, ans = 0, k = 0;
scanf("%lld", &n);
vector<int> a(n), b(n), c, d;
c.clear(); d.clear();
for(int i = 0; i < n; i++) cin>>a[i];
for(int i = 0; i < n; i++) cin>>b[i];
for(int i = 0; i < n; i++) {
if(a[i] > b[i]) {
for(int j = 1; j <= a[i] - b[i]; j++)
c.push_back(i);
}
else if(a[i] < b[i]) {
for(int j = 1; j <= b[i] - a[i]; j++)
d.push_back(i);
}
}
if(c.size() - d.size() != 0) cout << -1 << endl;
else {
cout << c.size() << endl;
for(int i = 0; i < c.size(); i++) {
cout << c[i] + 1 << " " << d[i] + 1 << endl;
}
}
return ;
}
signed main() {
int t; scanf("%lld", &t);
while(t--) solve();
return 0;
}
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