SRM 573 div2

250...

500...

1000

No idea during the competition. Instead, I thought of a trick. I wanted to take a cha. Later I found that no one in the room submitted it...

Only the number of pre-processed steps from one point to another, and the complexity of the DP space is too high. Today, I saw how others preprocessed it. I am still very tender...

DP [dx] [dy] [m] indicates the number of cases in which (dx, Dy) is moved by M-step coordinates.

Perform a memory search.

const int MAXN = 55;const int MOD = 1e9+7;int dp[MAXN][MAXN][MAXN];int dir[4][2] = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};class WolfPackDivTwo {public:    int dfs(int dx, int dy, int m) {        if(dp[dx][dy][m] != -1) return dp[dx][dy][m];        int res = 0;        if(m == 0) {            res = (dx == 0 && dy == 0);        } else {            for(int i = 0; i < 4; ++i) {                int xx = abs(dx + dir[i][0]);                int yy = abs(dy + dir[i][1]);                if(xx + yy > m - 1) continue;                res = (res + dfs(xx, yy, m - 1))%MOD;            }        }        return dp[dx][dy][m] = res;    }    int calc(vector <int> x, vector <int> y, int m) {        int n = x.size(), tx, ty, i, ans = 0;        CL(dp, -1);        for(tx = x[0] - m; tx <= x[0] + m; ++tx) {            for(ty = y[0] - m; ty <= y[0] + m; ++ty) {                int tmp = 1;                for(i = 0; i < n; ++i) {                    int dx = abs(tx - x[i]);                    int dy = abs(ty - y[i]);                    if(dx + dy > m) {tmp = 0; continue;}                    tmp = (tmp*dfs(dx, dy, m))%MOD;                }                ans = (ans + tmp)%MOD;            }        }        return ans;    }};