Submission #1636424

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Source Code Expand

#include <bits/stdc++.h>

using namespace std;

using ll = long long;

const int MAX_V = 300;

int V;
vector<int> G[MAX_V];
vector<int> rG[MAX_V];
vector<int> vs;
bool used[MAX_V];
int cmp[MAX_V];

void add_edge(int from, int to) {
    G[from].push_back(to);
    rG[to].push_back(from);
}

void dfs(int v) {
    used[v] = true;
    for (int i = 0; i < G[v].size(); i++) {
        if (!used[G[v][i]]) dfs(G[v][i]);
    }
    vs.push_back(v);
}

void rdfs(int v, int k) {
    used[v] = true;
    cmp[v] = k;
    for (int i = 0; i < rG[v].size(); i++) {
        if (!used[rG[v][i]]) rdfs(rG[v][i], k);
    }
}

int scc() {
    memset(used, 0, sizeof(used));
    vs.clear();
    for (int v = 0; v < V; v++) {
        if (!used[v]) dfs(v);
    }
    memset(used, 0, sizeof(used));
    int k = 0;
    for (int i = (int)vs.size() - 1; i >= 0; i--) {
        if (!used[vs[i]]) rdfs(vs[i], k++);
    }
    return k;
}

int n, m, k;
char c[305];
string ans[305][305];
string INF(400, 'z');
vector<char> buf;

void dfs2(int v) {
    used[v] = true;
    buf.push_back(c[v]);
    for (int i = 0; i < G[v].size(); i++) {
        if (!used[G[v][i]]) dfs2(G[v][i]);
        else if (cmp[v] != cmp[G[v][i]]) {
            for (int j = 1; j <= k; j++) {
                ans[cmp[v]][j] = min(ans[cmp[v]][j], ans[cmp[G[v][i]]][j]);
            }
        }
    }
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> n >> m >> k;
    V = n;
    for (int i = 0; i < n; i++) {
        cin >> c[i];
    }
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        a--;
        b--;
        add_edge(a, b);
    }
    scc();
    for (int i = 0; i < n; i++) {
        ans[i][0] = "";
        for (int j = 1; j <= k; j++) {
            ans[i][j] = INF;
        }
    }
    memset(used, 0, sizeof(used));
    string res = INF;
    for (int i = 0; i < vs.size(); i++) {
        if (used[vs[i]]) continue;
        buf.clear();
        int u = cmp[vs[i]];
        dfs2(vs[i]);
        sort(buf.begin(), buf.end());
        string tmp = "";
        for (char ch : buf) tmp += ch;
        for (int j = k; j >= 0; j--) {
            for (int l = 1; l <= min((int)tmp.size(), j); l++) {
                if (ans[u][j - l] == INF) continue;
                ans[u][j] = min(ans[u][j], tmp.substr(0, l) + ans[u][j - l]);
            }
        }
        res = min(res, ans[u][k]);
    }

    if (res == INF) cout << -1 << endl;
    else cout << res << endl;
    return 0;
}

Submission Info

Judge Result