HDU 2686 Matrix (双线程DP)

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http://acm.hdu.edu.cn/showproblem.php?pid=2686

双线程，嗯，好名字。

每次DFS传两个点的坐标，别让它们重合就行。

额外说一句，数据中有0

完整代码：

/*78ms,6112KB*/#include<cstdio>#include<cstring>#include<algorithm>using namespace std;const int mx = 35;const int dir[4][4] = {1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1};int dp[mx][mx][mx][mx], a[mx][mx], N;int f(int x1, int y1, int x2, int y2){if (a[x1][y1] == -1 || a[x2][y2] == -1) return 0;if (x1 == N && y1 == N) return a[N][N];if (dp[x1][y1][x2][y2] >= 0) return dp[x1][y1][x2][y2];if (x1 == x2 && y1 == y2 && x1 + y1 > 2) return 0;int ans = 0;for (int i = 0; i < 4; ++i)ans = max(ans, f(x1 + dir[i][0], y1 + dir[i][1], x2 + dir[i][2], y2 + dir[i][3]));return dp[x1][y1][x2][y2] = ans + a[x1][y1] + a[x2][y2];}int main(){int i, j;while (~scanf("%d", &N)){memset(a, -1, sizeof(a));for (i = 1; i <= N; ++i)for (j = 1; j <= N; ++j)scanf("%d", &a[i][j]);memset(dp, -1, sizeof(dp));printf("%d\n", f(1, 1, 1, 1) - a[1][1]);}return 0;}

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