UVa 11552 DP Fewest Flops

题解

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

const int maxn = 1000 + 10;
const int maxm = 30;

int n, k;

char s[maxn];
int d[maxn][maxm];

int cnt[maxn];
bool vis[maxn][maxm];

int main()
{
    int T; scanf("%d", &T);
    while(T--)
    {
        scanf("%d %s", &k, s);
        n = strlen(s);

        memset(d, 0x3f, sizeof(d));
        memset(cnt, 0, sizeof(cnt));
        memset(vis, false, sizeof(vis));
        for(int i = 0; i < n; i += k)
        {
            for(int j = 0; j < k; j++)
            {
                int ch = s[i + j] - 'a';
                if(!vis[i][ch]) cnt[i]++;
                vis[i][ch] = true;
            }
        }

        for(int i = 0; i < 26; i++) if(vis[0][i]) d[0][i] = cnt[0];

        for(int i = k; i < n; i += k)
            for(int j = 0; j < 26; j++) if(vis[i][j])
                for(int t = 0; t < 26; t++) if(vis[i - k][t])
                {
                    if(vis[i][t] && (j != t || cnt[i] == 1))
                        d[i][j] = min(d[i][j], d[i-k][t] + cnt[i] - 1);
                    else
                        d[i][j] = min(d[i][j], d[i-k][t] + cnt[i]);
                }

        int ans = n;
        for(int i = 0; i < 26; i++) ans = min(ans, d[n - k][i]);
        printf("%d
", ans);
    }

    return 0;
}