test=int(input())
while test:
n=int(input())
s1=input()
s2=input()
all_equal=0
for i,j in zip(s1,s2):
if(i==j):
all_equal+=1
if(all_equal==0 or all_equal==n):
print("YES")
ones=s1.count('1')
if((all_equal==n and ones%2!=0) or (all_equal==0 and ones%2==0)):
print(ones+3)
else:
print(ones)
for i in range(n):
if(s1[i]=='1'):
print(i+1,i+1)
if((all_equal==n and ones%2!=0) or (all_equal==0 and ones%2==0)):
print(1,1)
print(2,n)
print(1,n)
else:
print("NO")
test-=1
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define mod 1000000007
#define int long long
void solve(){
int n; cin>>n;
string a, b; cin>>a>>b;
int diff = abs(a[0] - b[0]);
for(int i = 0; i < n; i++){
if(abs(a[i] - b[i]) != diff){
cout<<"NO"<<endl;
return;
}
}
cout<<"YES"<<endl;
int aones = 0, azeros = 0, bzeros = 0, bones = 0;
for(auto &x : a){
if(x == '1') aones++;
else azeros++;
}
for(auto &x : b){
if(x == '1') bones++;
else bzeros++;
}
if(bones == n){
if(aones == n){
cout<<"2"<<endl;
cout<<1<<" "<<1<<endl;
cout<<2<<" "<<n<<endl;
return;
}
else{
cout<<"3"<<endl;
cout<<1<<" "<<n<<endl;
cout<<1<<" "<<1<<endl;
cout<<2<<" "<<n<<endl;
return;
}
}
if(bones == 0){
if(aones == 0){
cout<<"0"<<endl;
return;
}
else{
cout<<"1"<<endl;
cout<<1<<" "<<n<<endl;
return;
}
}
vector<int> zeros;
for(int i = 0; i < n; i++) if(a[i] == '0') zeros.push_back(i + 1);
azeros = azeros - ((a[0] == '0') ? 1 : 0);
// cout<<azeros<<" ->>>> "<<endl;
if(azeros % 2 == 0){
// all b toggles acc to b[0].
if(b[0] == '0'){
//all b becomes 0.
cout<<zeros.size() + 1<<endl;
for(auto &x : zeros) cout<<x<<" "<<x<<endl;
cout<<1<<" "<<n<<endl;
}
else{
//all b becomes 1.
cout<<zeros.size() + 2<<endl;
for(auto &x : zeros) cout<<x<<" "<<x<<endl;
cout<<1<<" "<<1<<endl;
cout<<2<<" "<<n<<endl;
}
}
else{
if(b[0] == '0'){
//all b becomes 1.
cout<<zeros.size() + 2<<endl;
for(auto &x : zeros) cout<<x<<" "<<x<<endl;
cout<<1<<" "<<1<<endl;
cout<<2<<" "<<n<<endl;
}
else{
//all b becomes 0.
cout<<zeros.size() + 1<<endl;
for(auto &x : zeros) cout<<x<<" "<<x<<endl;
cout<<1<<" "<<n<<endl;
}
}
}
int32_t main (){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int t = 1;
cin>>t;
while(t--){
solve();
}
return 0;
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