HDU 5617 Jam's maze dp+滚动数组

题目链接：

hdu: http://acm.hdu.edu.cn/showproblem.php?pid=5617

bc(中文):http://bestcoder.hdu.edu.cn/contests/contest_chineseproblem.php?cid=666&pid=1003

题解：

设dp[x1][x2][i]表示第i步时，从（1,1)点走到了(x1,y1)，（n,n）点走到了(x2,y2)点的合法的总数。

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 using namespace std;
 5
 6 const int maxn = 505;
 7 const int mod = 5201314;
 8
 9 int dp[maxn][maxn][2];
10 char str[maxn][maxn];
11
12 int n;
13
14 void init() {
15     memset(dp, 0, sizeof(dp));
16 }
17
18 inline int add(int x, int y) {
19     x += y;
20     if (x > mod) x -= mod;
21     return x;
22 }
23
24 int main() {
25     int tc;
26     scanf("%d", &tc);
27     while (tc--) {
28         init();
29         scanf("%d", &n);
30         for (int i = 1; i <= n; i++) scanf("%s", str[i] + 1);
31         if (str[1][1] == str[n][n]) dp[1][n][0] = 1;
32         //printf("dp[1][n][0]:%d\n", dp[1][n][0]);
33         int u = 1;
34         for (int i = 2; i <= n; i++) {
35             for (int j = 1; j <= i; j++) {
36                 for (int k = 1; k <= i; k++) {
37                     int x1, y1, x2, y2;
38                     x1 = j; y1 = i + 1 - x1;
39                     x2 = n + 1 - k; y2 = 2 * n - i + 1 - x2;
40
41                     //滚动数组非常需要注意的地方就是！！！每次都要初始化！！！初始化！！！初始化！！！
42                     dp[x1][x2][u] = 0;
43
44                     //if (i == n&&x1 != x2) continue;
45
46                     if (str[x1][y1] == str[x2][y2]) {
47                         //printf("fuck!");
48                         int &cur = dp[x1][x2][u];
49                         cur = add(cur, dp[x1][x2][!u]);
50                         cur = add(cur, dp[x1][x2 + 1][!u]);
51                         cur = add(cur, dp[x1 - 1][x2][!u]);
52                         cur = add(cur, dp[x1- 1][x2 + 1][!u]);
53                     }
54                 }
55             }
56             u = !u;
57         }
58         int ans = 0;
59         for (int i = 1; i <= n; i++) ans = add(ans, dp[i][i][!u]);
60         printf("%d\n", ans);
61     }
62     return 0;
63 }

HDU 5617 Jam's maze dp+滚动数组