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Educational Codeforces Round 34 (Rated for Div. 2)/E. Swapping Characters.cpp

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+/* Problem URL: https://codeforces.com/contest/903/problem/E */
+
+#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;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int n, k;
+    cin >> k >> n;
+
+    V<string> fds(k);
+    cin >> fds;
+
+    vi diffs;
+
+    int other = 0;
+
+    vi c1(26);
+    rep(i, n) {
+        c1[fds[0][i] - 'a']++;
+    }
+
+    nrep(i, 1, k) {
+        vi c2(26);
+        rep(j, n) {
+            if (fds[0][j] != fds[i][j]) {
+                diffs.push_back(j);
+            }
+            c2[fds[i][j] - 'a']++;
+        }
+
+        if (c1 != c2) {
+            cout << "-1\n";
+            return 0;
+        }
+
+        if (!diffs.empty()) {
+            other = i;
+            break;
+        }
+    }
+
+    if (diffs.empty()) {
+        swap(fds[0][0], fds[0][1]);
+        cout << fds[0] << '\n';
+        return 0;
+    }
+
+    if (diffs.size() > 4) {
+        cout << "-1\n";
+        return 0;
+    }
+
+    string now = fds[0];
+    auto test = [&]() {
+        rep(i, diffs.size()) {
+            rep(j, n) {
+                if (diffs[i] == j) {
+                    continue;
+                }
+                swap(now[diffs[i]], now[j]);
+
+                auto diff = [&](string &a, string &b) {
+                    vi count(26);
+                    bool lmao = false;
+
+                    int ans = 0;
+                    rep(i, n) {
+                        count[a[i] - 'a']++;
+                        lmao = lmao || count[a[i] - 'a'] >= 2;
+                        if (a[i] != b[i]) {
+                            ans++;
+                        }
+                    }
+
+                    return ans == 2 || (ans == 0 && lmao);
+                };
+
+                bool pos = true;
+
+                rep(l, k) {
+                    int d = diff(now, fds[l]);
+                    if (!diff(now, fds[l])) {
+                        pos = false;
+                        break;
+                    }
+                }
+
+                if (pos) {
+                    return true;
+                }
+
+                swap(now[diffs[i]], now[j]);
+            }
+        }
+
+        return false;
+    };
+
+    if (test()) {
+        cout << now << '\n';
+        return 0;
+    }
+
+    now = fds[other];
+
+    if (test()) {
+        cout << now << '\n';
+        return 0;
+    }
+
+    cout << "-1\n";
+}