UVA11552 Fewest Flops

#include <bits/stdc++.h>
#define maxn 1100
#define INF 0x3f3f3f3f
typedef long long ll;
using namespace std;
char s[maxn];
int num[maxn], dp[maxn][30], mp[maxn][30];
int main(){
    int T, x, n, l, ans;
    scanf("%d", &T);
    while(T--){
        scanf("%d", &x);
        scanf("%s", s);
        l = strlen(s);
        n = l/x;
        memset(mp, 0, sizeof(mp));
        memset(num, 0, sizeof(num));
        memset(dp, INF, sizeof(dp));
        for(int i=0;i<l;i++){
            if(mp[i/x][s[i]-‘a‘] == 0) num[i/x]++;
            mp[i/x][s[i]-‘a‘]++;
        }
        for(int i=0;i<=25;i++)
            if(mp[0][i]){
                dp[0][i] = num[0];
            }
        for(int i=1;i<n;i++){
            for(int k=0;k<=25;k++){
                if(mp[i-1][k] == 0) continue;
                for(int j=0;j<=25;j++){
                    if(mp[i][j] == 0) continue;
                    for(int t=0;t<=25;t++){
                        if(mp[i][t] == 0) continue;
                        if(t==j&&num[i]!=1) continue;
                        if(k == t) dp[i][j] = min(dp[i][j], dp[i-1][k]+num[i]-1);
                        else dp[i][j] = min(dp[i][j], dp[i-1][k]+num[i]);
                    }
                }
            }
        }
        ans = INF;
        for(int i=0;i<=25;i++){
            ans = min(ans, dp[n-1][i]);
        }
        printf("%d\n", ans);
    }
    return 0;
}