1196D2

1196D2 - RGB Substring (hard version)

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <set>
#include <queue>
#include <map>
#include <sstream>
#include <cstdio>
#include <cstring>
#include <numeric>
#include <cmath>
#include <iomanip>
#include <deque>
#include <bitset>
//#include <unordered_set>
//#include <unordered_map>
#define ll              long long
#define pii             pair<int, int>
#define rep(i,a,b)      for(ll  i=a;i<=b;i++)
#define dec(i,a,b)      for(ll  i=a;i>=b;i--)
#define forn(i, n)      for(ll i = 0; i < int(n); i++)
using namespace std;
int dir[4][2] = { { 1,0 },{ 0,1 } ,{ 0,-1 },{ -1,0 } };
const long long INF = 0x7f7f7f7f7f7f7f7f;
const int inf = 0x3f3f3f3f;
const double pi = 3.14159265358979323846;
const double eps = 1e-6;
const int mod = 1e7 + 7;

inline ll read()
{
    ll x = 0; bool f = true; char c = getchar();
    while (c < '0' || c > '9') { if (c == '-') f = false; c = getchar(); }
    while (c >= '0' && c <= '9') x = (x << 1) + (x << 3) + (c ^ 48), c = getchar();
    return f ? x : -x;
}
inline ll gcd(ll m, ll n)
{
    return n == 0 ? m : gcd(n, m % n);
}
void exgcd(ll A, ll B, ll& x, ll& y)
{
    if (B) exgcd(B, A % B, y, x), y -= A / B * x; else x = 1, y = 0;
}

bool prime(int x) {
    if (x < 2) return false;
    for (int i = 2; i * i <= x; ++i) {
        if (x % i == 0) return false;
    }
    return true;
}
inline int qpow(int x, ll n) {
    int r = 1;
    while (n > 0) {
        if (n & 1) r = 1ll * r * x % mod;
        n >>= 1; x = 1ll * x * x % mod;
    }
    return r;
}
/**********************************************************/
int len , n;
int solve(string& s,string& t)
{
    vector<int> v(len);
    int cnt =0;
    forn(i,len)
    {
        if(s[i]!=t[i])
            v[i]=1;
    }
    int i=0,j=0;
    while(j<n)
    {
        if(v[j]==1)
            cnt++;
        j++;
    }
    int ans=inf;
    while(j<len)
    {
        ans=min(ans,cnt);
        if(j<len)
            cnt+=-v[i]+v[j];
        i++,j++;
    }
    ans=min(ans,cnt);
    return ans;
}
int main(){
    int T;
    cin>>T;
    while(T--)
    {
        cin>>len>>n;
        string s;
        cin>>s;
        string t;
        for(int i=0;i<len;i++)
        {
            if(i%3==0)
                t+='R';
            else if (i%3==1)
                t+='G';
            else
                t+='B';
        }
        int ans=inf;
        ans=min(ans,solve(s,t));
        rep(i,0,1)
        {
            t.erase(0,1);
            if((len+i)%3==0)
                t+='R';
            else if ((len+i)%3==1)
                t+='G';
            else
                t+='B';
            ans=min(ans,solve(s,t));
        }
        cout<<ans<<endl;
    }

}

 尺取的时候长度应该是n+1