[백준 1068번] 트리

소스코드

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#include <iostream>
using namespace std;
 
int n, rm, tr[51][51] = { 0, }, visit[51][51] = { 0, }, root[51] = {0,};
int q[10001], h = 0, t = 0, cnt=0;
 
void bfs() {
    while (h != t) {
        int cur = q[h++];
        int flag = 0;
        for (int i = 0; i < n; i++) {
            if (tr[cur][i] == 1 && visit[cur][i]==0) {
                flag = 1;
                visit[cur][i] = 1;
                q[t++] = i;
            }
        }
        if (!flag && !root[cur]) {
            cnt++;
        }
    }
}
 
int main() {
    cin >> n;
    for (int i = 0; i < n; i++) {
        int in;
        cin >> in;
        if (in == -1) {
            q[t++] = i;
            root[i] = 1;
            continue;
        }
        tr[in][i] = 1;
    }
    cin >> rm;
    for (int i = 0; i < n; i++) {
        tr[rm][i] = 0;
        tr[i][rm] = 0;
    }
    bfs();
    cout << cnt << '\n';
    return 0;
}