toj 4070 简单dp

相当于是在求最短路，该序列为拓扑有序（线性序列），所以可以直接dp。

 1 #include <iostream>

 2 #include <cstring>

 3 #include <cstdio>

 4 using namespace std;

 5 

 6 const int INF = 1 << 29;

 7 const int N = 21;

 8 char road[N];

 9 int cost[N];

10 

11 void init()

12 {

13     cost[0] = 0;

14     for ( int i = 1; i < N; i++ ) cost[i] = INF;

15 }

16 

17 bool check( int i, int j )

18 {

19     if ( road[i] == 'R' && road[j] == 'G' ) return true;

20     if ( road[i] == 'G' && road[j] == 'B' ) return true;

21     if ( road[i] == 'B' && road[j] == 'R' ) return true;

22     return false;

23 }

24 

25 int main ()

26 {

27     int t;

28     scanf("%d", &t);

29     while ( t-- )

30     {

31         scanf("%s", road);

32         int len = strlen(road);

33         init();

34         for ( int i = 0; i < len - 1; i++ )

35         {

36             for ( int j = i + 1; j < len; j++ )

37             {

38                 if ( check( i, j ) )

39                 {

40                     int tmp = cost[i] + ( j - i ) * ( j - i );

41                     if ( tmp < cost[j] ) cost[j] = tmp;

42                 }

43             }

44         }

45         if ( cost[len - 1] == INF ) cost[len - 1] = -1;

46         printf("%d\n", cost[len - 1]);

47     }

48     return 0;

49 }