HDU 5903 - Square Distance [ DP ] ( BestCoder Round #87 1002 )

 1 #include <cstdio>
 2 #include <algorithm>
 3 #include <iostream>
 4 #include <cstring>
 5 using namespace std;
 6 const int MAXN = 1005;
 7 bool dp[MAXN][MAXN];//dp[i][j] ：第i位及之后的总代价为j可不可行 
 8 int t, n, m;
 9 char s[MAXN];
10 int main()
11 {
12     scanf("%d", &t);
13     while (t--)
14     {
15         scanf("%d%d", &n, &m);
16         scanf("%s", s);
17         memset(dp, 0, sizeof(dp));
18         dp[n/2][0] = 1;
19         for (int i = n/2-1; i >= 0; i--)
20         {
21             if (s[i] == s[i+n/2])
22             {
23                 for (int j = 0; j <= m; j++) dp[i][j] = dp[i+1][j];//不改
24                 for (int j = 0; j <= m-2; j++) if (dp[i+1][j]) dp[i][j+2] = 1;//改两个
25             }
26             else
27             {
28                 for (int j = 0; j <= m-1; j++) if (dp[i+1][j]) dp[i][j+1] = 1;//改一个
29                 for (int j = 0; j <= m-2; j++) if (dp[i+1][j]) dp[i][j+2] = 1;//改两个
30             }
31         }
32         if (!dp[0][m])
33         {
34             puts("Impossible"); continue;
35         }
36         int k = m;
37         for (int i = 0; i < n/2; i++)
38         {
39             for (int j = 0; j < 26; j++)
40             {
41                 int p = 0;
42                 if (s[i] != j+‘a‘) p++;
43                 if (s[i+n/2] != j+‘a‘) p++;
44                 if (dp[i+1][k-p])
45                 {
46                     s[i] = j + ‘a‘;
47                     s[i+n/2] = j + ‘a‘;
48                     k -= p;
49                     break;
50                 }
51             }
52         }
53         puts(s);
54     }
55 }