HDU 4455 Substrings ( DP好题 )

这个……真心看不出来是个DP，我在树状数组的康庄大道上欢快的奔跑了一下午……看了题解才发现错的有多离谱。

参考：http://www.cnblogs.com/kuangbin/archive/2012/11/11/2765329.html

 

#include <cstdio>

#include <cstring>

#include <cstdlib>

#include <algorithm>



#define LL long long int



using namespace std;



const int MAXN = 1000100;



int val[MAXN];

int pos[MAXN];

int cnt[MAXN];

int diff[MAXN];

bool vis[MAXN];

LL dp[MAXN];

int N;



int main()

{

    while ( scanf( "%d", &N ) == 1 && N )

    {

        memset( cnt, 0, sizeof(int)*(N+4) );

        memset( pos, 0, sizeof(int)*(N+4) );



        for ( int i = 1; i <= N; ++i )

        {

            scanf( "%d", &val[i] );

            ++cnt[ i - pos[ val[i] ] ];

            pos[ val[i] ] = i;

        }



        memset( vis, false, sizeof(bool)*(N+4) );

        diff[1] = 1;

        vis[ val[N] ] = true;

        for ( int i = 2; i <= N; ++i )

        {

            if ( vis[ val[N-i+1] ] )

                diff[i] = diff[i - 1];

            else

            {

                diff[i] = diff[i - 1] + 1;

                vis[ val[N-i+1] ] = true;

            }

        }



        int tot = N;

        dp[1] = N;

        for ( int i = 2; i <= N; ++i )

        {

            dp[i] = dp[i - 1] - diff[i - 1];

            tot -= cnt[i - 1];

            dp[i] += tot;

        }



        int Q;

        scanf("%d", &Q );

        while ( Q-- )

        {

            int w;

            scanf("%d", &w);

            printf("%I64d\n", dp[w] );

        }

    }

    return 0;

}