Code : Colored Portals

#include <bits/stdc++.h>
using namespace std;

const int inf = 1e8;

void solve() {
    int n, q;
    cin >> n >> q;

    vector<int> a(n + 1, 0);
    map<char, int> index;
    index['R'] = 0, index['G'] = 1, index['B'] = 2, index['Y'] = 3;
    for (int i = 1; i <= n; i++) {
        int mask = 0;
        string str;
        cin >> str;
        for (auto &ch : str) {
            mask |= (1 << index[ch]);
        }
        a[i] = mask;
    }

    // ldp[i] is the closest node to the left with exactly one common bit.
    vector<int> ldp(n + 1, -1);
    map<int, int> last;
    for (int i = 1; i <= n; i++) {
        for (auto &[mask, ind] : last) {
            if (__builtin_popcount(mask & a[i]) == 1) {
                ldp[i] = max(ldp[i], ind);
            }
        }
        last[a[i]] = i;
    }

    // rdp[i] is the closest node to the right with exactly one common bit.
    vector<int> rdp(n + 1, inf);
    last.clear();
    for (int i = n; i >= 1; i--) {
        for (auto &[mask, ind] : last) {
            if (__builtin_popcount(mask & a[i]) == 1) {
                rdp[i] = min(rdp[i], ind);
            }
        }
        last[a[i]] = i;
    }

    while (q--) {
        int x, y;
        cin >> x >> y;
        if (x > y) {
            swap(x, y);
        }
        int dist = abs(x - y);
        if ((a[x] & a[y]) == 0) {
            int delta = inf;
            if (ldp[x] != -1) {
                delta = min(delta, 2 * (x - ldp[x]));
            }
            if (rdp[x] != inf) {
                delta = min(delta, 2 * (max(0, rdp[x] - y)));
            }
            dist += delta;
        }

        if (dist >= inf) {
            cout << -1 << "\n";
        } else {
            cout << dist << "\n";
        }
    }
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int t;
    cin >> t;
    while (t--) {
        solve();
    }
}