Codeforces1196D2

字符串长度2e5
前缀和子串长度维护k 到后-前面的前缀和

#include<bits/stdc++.h>
#include<deque>
using namespace std;
#define IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)#define forn(i,n)  for(int i=0;i<n;i++)
#define rep(i,a,n) for(int i=a;i<=n;i++)
#define mp make_pair
#define pb push_back
#define fi first
#define se secondtypedef long long ll;
const int maxn=2e5+5;
const int INF=0x3f3f3f3f;
const ll inf=0x3f3f3f3f3f3f3f3f;
const int mod=1e9+7;int q,n,k;
string s,t="RGB";
int main()
{cin>>q;while(q--){cin>>n>>k;cin>>s;int ans=1e9;for(int i=0;i<3;i++){int cur=0;vector<int> res(n);for(int j=0;j<n;j++){res[j]=(s[j]!=t[(i+j)%3]);cur+=res[j];if(j>=k)cur-=res[j-k];if(j>=k-1)ans=min(ans,cur);}}cout<<ans<<endl;}return 0;
}

dp[3][maxn] 3种情况长度=6e5
先构造 “RGB” “GBR” “BRG” 长度为n的字符串
三种情况与s比较不同计数前缀和
3种情况分别有结尾k->n的子串取min

#include<bits/stdc++.h>
#include<deque>
using namespace std;
#define IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)#define forn(i,n)  for(int i=0;i<n;i++)
#define rep(i,a,n) for(int i=a;i<=n;i++)
#define mp make_pair
#define pb push_back
#define fi first
#define se secondtypedef long long ll;
const int maxn=2e5+5;
const int INF=0x3f3f3f3f;
const ll inf=0x3f3f3f3f3f3f3f3f;
const int mod=1e9+7;int q,n,m,k,ans;char s[maxn];
int dp[3][maxn];
char t[3][maxn],a[]={'R','G','B'};
int main()
{scanf("%d",&q);while(q--){scanf("%d %d %s",&n,&k,s+1);for(int i=0;i<3;i++){for(int j=1;j<=n;j++){t[i][j]=a[(i+j)%3];}t[i][n+1]='\0';}for(int i=0;i<3;i++){for(int j=1;j<=n;j++){dp[i][j]=dp[i][j-1]+(s[j]!=t[i][j]);}}ans=n; for(int i=0;i<3;i++){for(int j=k;j<=n;j++){     //枚举子串ans=min(ans,dp[i][j]-dp[i][j-k]);}}cout<<ans<<endl;}return 0;
}

Codeforces1196D2

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