Codeforces-solutions/Codeforces Round 1067 (Div. 2)/D. Palindrome Flipping.cpp

/* Problem URL: https://codeforces.com/contest/2158/problem/D */

#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;

template <class T, class comp = less<>>
using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;

#define V vector

#define rmin(a, b) a = min(a, b)
#define rmax(a, b) a = max(a, b)

#define rep(i, lim) for (int i = 0; i < (lim); i++)
#define nrep(i, s, lim) for (int i = s; i < (lim); i++)

#define repv(i, v) for (auto &i : (v))
#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
#define sortv(v) sort(v.begin(), v.end())
#define all(v) (v).begin(), (v).end()

using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vvvvi = vector<vvvi>;

using ll = long long;

using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vvvvl = vector<vvvl>;

template<class v>
auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
    os << vec[0];
    for (size_t i = 1; i < vec.size(); i++) {
        os << ' ' << vec[i];
    }
    os << '\n';
    return os;
}

template<class v>
auto operator>>(istream &is, vector<v> &vec)->istream& {
    for (auto &i : vec) {
        is >> i;
    }
    return is;
}

template<class v>
auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
    for (auto &i : vec) {
        os << i[0];
        for (size_t j = 1; j < i.size(); j++) {
            os << ' ' << i[j];
        }
        os << '\n';
    }
    return os;
}

template<class v>
auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
    for (auto &i : vec) {
        for (auto &j : i) {
            is >> j;
        }
    }
    return is;
}

const int oo = INT32_MAX >> 1;
const ll OO = INT64_MAX >> 1;


map<string, pair<V<pair<int, int>>, char>> ops;
map<string, V<pair<int, int>>> getlast[2];
void pre()
{
    ops["0000"] = {{}, '0'};
    ops["0001"] = {{{1, 3}}, '1'};
    ops["0010"] = {{{1, 2}, {1, 3}}, '0'};
    ops["0011"] = {{{1, 2}}, '1'};
    ops["0100"] = {{{3, 4}, {2, 4}}, '0'};
    ops["0101"] = {{{1, 3}, {3, 4}, {2, 4}}, '1'};
    ops["0110"] = {{{2, 3}}, '0'};
    ops["0111"] = {{{2, 4}}, '0'};
    ops["1000"] = {{{2, 4}}, '1'};
    ops["1001"] = {{{2, 3}}, '1'};
    ops["1010"] = {{{1, 3}, {3, 4}, {2, 4}}, '0'};
    ops["1011"] = {{{3, 4}, {2, 4}}, '1'};
    ops["1100"] = {{{1, 2}}, '0'};
    ops["1101"] = {{{1, 2}, {1, 3}}, '1'};
    ops["1110"] = {{{1, 3}}, '0'};
    ops["1111"] = {{}, '1'};

    getlast[0]["0000"] = {};
    getlast[0]["0001"] = {{1, 4}, {1, 3}};
    getlast[0]["0010"] = {{1, 3}, {1, 2}};
    getlast[0]["0011"] = {{3, 4}};
    getlast[0]["0100"] = {{2, 4}, {3, 4}};
    getlast[0]["0101"] = {{1, 3}, {1, 2}, {2, 4}};
    getlast[0]["0110"] = {{2, 3}};
    getlast[0]["0111"] = {{2, 4}};
    getlast[0]["1000"] = {{1, 4}, {2, 4}};
    getlast[0]["1001"] = {{2, 3}, {1, 4}};
    getlast[0]["1010"] = {{2, 4}, {3, 4}, {1, 3}};
    getlast[0]["1011"] = {{1, 4}, {2, 4}, {3, 4}};
    getlast[0]["1100"] = {{1, 2}};
    getlast[0]["1101"] = {{1, 4}, {1, 3}, {1, 2}};
    getlast[0]["1110"] = {{1, 3}};
    getlast[0]["1111"] = {{1, 4}};

    getlast[1]["1111"] = {};
    getlast[1]["1110"] = {{1, 4}, {1, 3}};
    getlast[1]["1101"] = {{1, 3}, {1, 2}};
    getlast[1]["1100"] = {{3, 4}};
    getlast[1]["1011"] = {{2, 4}, {3, 4}};
    getlast[1]["1010"] = {{1, 3}, {1, 2}, {2, 4}};
    getlast[1]["1001"] = {{2, 3}};
    getlast[1]["1000"] = {{2, 4}};
    getlast[1]["0111"] = {{1, 4}, {2, 4}};
    getlast[1]["0110"] = {{2, 3}, {1, 4}};
    getlast[1]["0101"] = {{2, 4}, {3, 4}, {1, 3}};
    getlast[1]["0100"] = {{1, 4}, {2, 4}, {3, 4}};
    getlast[1]["0011"] = {{1, 2}};
    getlast[1]["0010"] = {{1, 4}, {1, 3}, {1, 2}};
    getlast[1]["0001"] = {{1, 3}};
    getlast[1]["0000"] = {{1, 4}};
}

#define TEST 1

void solve()
{
    int n;
    cin >> n;
    string a, b;
    cin >> a >> b;

    auto [ans, cur] = ops[a.substr(0, 4)];

    nrep(i, 4, n) {
        if (a[i] != cur) {
            ans.emplace_back(1, i);
            cur = a[i];
        }
    }

    for (int i = n - 1; i > 3; i--) {
        if (b[i] != cur) {
            ans.emplace_back(1, i + 1);
            cur = b[i];
        }
    }

    auto bf = getlast[cur - '0'][b.substr(0, 4)];
    repv(i, bf) {
        ans.emplace_back(i);
    }

    cout << ans.size() << '\n';
    repv(i, ans) {
        cout << i.first << ' ' << i.second << '\n';
    }
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    pre();

    int t;
    (TEST && cin >> t) || (t = 1);
    while (t--) {
        solve();
    }
}