find cycle

#include <iostream>
using namespace std;
int n, m, a[101][101], vis[101], ok;

void dfs(int i) {
    vis[i] = 1;
    for (int j = 1; j <= n; j++)
        if (a[i][j]) {
            a[i][j] = a[j][i] = 0;
            if (vis[j])
                ok = 1;
            else
                dfs(j);
        }
}

int main() {
    cin >> n >> m;
    int x, y;
    for (int i = 1; i <= m; i++) {
        cin >> x >> y;
        a[x][y] = a[y][x] = 1;
    }
    dfs(1);
    if (ok)
        cout << "DA";
    else
        cout << "NU";
    return 0;
}