poj3740

dfs

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#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

#define maxn 20
#define maxm 305

int n, m;
int map[maxn][maxm];
int num[maxn];
bool g[maxn][maxn];
int rownum[maxn];
bool found;

void input()
{
    memset(num, 0, sizeof(num));
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++)
        {
            int a;
            scanf("%d", &a);
            if (a == 0)
                map[i][j] = 0;
            else
            {
                map[i][j] = 1;
                num[i]++;
            }
        }
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
        {
            bool ok = true;
            for (int k = 0; k < m; k++)
                if (map[i][k] && map[j][k])
                {
                    ok = false;
                    break;
                }
            if (ok)
                g[i][j] = true;
            else
                g[i][j] = false;
        }
}

void dfs(int tot, int now, int ans)
{
    if (found)
        return;
    if (now == n)
    {
        if (ans == m)
            found = true;
        return;
    }
    dfs(tot, now + 1, ans);
    bool ok = true;
    for (int i = 0; i < tot; i++)
        if (!g[rownum[i]][now])
        {
            ok = false;
            break;
        }
    if (ok)
    {
        rownum[tot] = now;
        dfs(tot + 1, now + 1, ans + num[now]);
    }
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (scanf("%d%d", &n, &m) != EOF)
    {
        found = false;
        input();
        dfs(0, 0, 0);
        if (found)
            printf("Yes, I found it\n");
        else
            printf("It is impossible\n");
    }
    return 0;
}