路径之谜（2016蓝桥杯国赛）

#include
using namespace std;

typedef pair PII;
const int N = 30;
int row[N], col[N];
int n;
vector path;
int dx[] = {-1,0,1,0}, dy[] = {0,1,0,-1};

bool st[N][N];

bool check()
{
    for (int i = 0; i < n; i++)
    {
        if (row[i] || col[i]) return false;//行或列箭数量不够，非0
    }
    return true;
}

void dfs(int x,int y)
{
    row[x]--, col[y]--;//这一点行列箭的数量其实是+1表面-1
    st[x][y] = true;//表示此点走过了
    path.push_back({ x,y });//先将这个点放到当前路径中

    if (row[x] < 0 || col[y] < 0) return;
    if (x == n - 1 && y == n - 1 && check())
    {
        for (int i = 0; i < path.size(); i++)
        {
            cout << n * path[i].first + path[i].second << " ";
        }
        exit(0);
    }

    for (int i = 0; i < 4; i++)
    {
        int a = x + dx[i], b = y + dy[i];
        if (a < 0 || b < 0 || a >= n || b >= n) continue;//越界剪掉
        if (st[a][b]) continue;//走过剪掉
        dfs(a, b);//从这个点在开始搜素

        //回溯剪枝恢复原始状态
        path.pop_back();
        row[a]++, col[b]++;
        st[a][b] = false;
    }
}
int main()
{
    cin >> n;
    for (int i = 0; i < n; i++) cin >> col[i];
    for (int i = 0; i < n; i++) cin >> row[i];
    dfs(0, 0);
    return 0;
}