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。

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

 const int maxn = ;
 const int mod = ;

 int dp[maxn][maxn][];
 char str[maxn][maxn];

 int n;

 void init() {
     memset(dp, , sizeof(dp));
 }

 inline int add(int x, int y) {
     x += y;
     if (x > mod) x -= mod;
     return x;
 }

 int main() {
     int tc;
     scanf("%d", &tc);
     while (tc--) {
         init();
         scanf("%d", &n);
         for (int i = ; i <= n; i++) scanf("%s", str[i] + );
         if (str[][] == str[n][n]) dp[][n][] = ;
         //printf("dp[1][n][0]:%d\n", dp[1][n][0]);
         int u = ;
         for (int i = ; i <= n; i++) {
             for (int j = ; j <= i; j++) {
                 for (int k = ; k <= i; k++) {
                     int x1, y1, x2, y2;
                     x1 = j; y1 = i +  - x1;
                     x2 = n +  - k; y2 =  * n - i +  - x2;

                     //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！！！
                     dp[x1][x2][u] = ;

                     //if (i == n&&x1 != x2) continue;

                     if (str[x1][y1] == str[x2][y2]) {
                         //printf("fuck!");
                         int &cur = dp[x1][x2][u];
                         cur = add(cur, dp[x1][x2][!u]);
                         cur = add(cur, dp[x1][x2 + ][!u]);
                         cur = add(cur, dp[x1 - ][x2][!u]);
                         cur = add(cur, dp[x1- ][x2 + ][!u]);
                     }
                 }
             }
             u = !u;
         }
         int ans = ;
         for (int i = ; i <= n; i++) ans = add(ans, dp[i][i][!u]);
         printf("%d\n", ans);
     }
     return ;
 }