暴力 hihoCoder 1251 Today Is a Rainy Day (15北京C)

 

题目传送门

题意：一串数字变成另一串数字，可以单个数字转变，或者一类数字转变，问最少操作次数

分析：首先一类转换比单个转换优，先枚举找出最优的映射方案，然后将零碎的操作加上。6位6进制表示map映射，比如123456，表示map[1] = 1, map[2] = 2, map[3] = 3...

先预处理出每种方案的的操作数，用BFS+dp写，然后暴力枚举取最小值。

 

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#include <bits/stdc++.h> using namespace std;   const int N = 110 + 5; const int M = 5e4 + 5; const int INF = 0x3f3f3f3f; char ori[N], fin[N]; int dp[M]; int cnt[6]; int g[6][6];   int idx(int *c) {     int ret = 0;     for (int i=0; i<6; ++i)  {         ret = ret * 6 + c[i];     }     return ret; }   void ridx(int x, int *c)    {     for (int i=5; i>=0; --i) {         c[i] = x % 6;         x /= 6;     } }   void BFS(void)  {     memset (dp, INF, sizeof (dp));     int c[6];     for (int i=0; i<6; ++i)  c[i] = i;   //nomal, not change     int s = idx (c);    dp[s] = 0;     queue<int> que;   que.push (s);     while (!que.empty ())   {         int u = que.front ();   que.pop ();         ridx (u, c);         for (int i=0; i<6; ++i)  {             for (int j=0; j<6; ++j)  {                 int t[6];                 memcpy (t, c, sizeof (t));                 for (int k=0; k<6; ++k)  {                     if (t[k] == i)  t[k] = j;                 }                 int v = idx (t);                 if (dp[v] > dp[u] + 1)   {                     dp[v] = dp[u] + 1;                     que.push (v);                 }             }         }     } }   int main(void)  {     BFS ();     while (scanf ("%s%s", ori, fin) == 2)   {         int len = strlen (ori);         memset (cnt, 0, sizeof (cnt));         memset (g, 0, sizeof (g));         for (int i=0; i<len; ++i)    {             int d1 = fin[i] - '1', d2 = ori[i] - '1';             cnt[d1]++;  g[d1][d2]++;         }         int ans = INF;         int c[6];         for (int i=0; i<M; ++i)  {             ridx (i, c);             int tmp = dp[i];             for (int j=0; j<6; ++j)  {                 tmp += cnt[j] - g[j][c[j]];             }             ans = min (ans, tmp);         }         printf ("%d\n", ans);     }       return 0; } /* 22345611 12345611 2234562221 1234561221 2234562211 1234561111 22345622112 12345611111 654321654321654321654321 123456123456123456123456 */