D - RGB Triplets

Posted 2021-03-01 asunayi

 

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Time Limit: 2 sec / Memory Limit: 1024 MB

ps:我的vector需要加强，用错了。

Problem Statement

We have a string $\mathrm{SS}$ of length $N$consisting of R, G, and B.

Find the number of triples $(i, j, k) (1\le i<j<k\le N)$that satisfy both of the following conditions:

• ${\mathrm{Si\ne Sj}}^{}$, ${\mathrm{Si\ne Sk}}^{}$, and ${\mathrm{Sj\ne Sk}}^{}$.
• $\mathrm{j-i\ne k-j}$.

Constraints

• $\mathrm{1\le N\le 40001\le N\le 4000}$
• $\mathrm{SS}$ is a string of length $\mathrm{NN}$ consisting of R, G, and B.

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Input

Input is given from Standard Input in the following format:

$N$
$S$

Output

Print the number of triplets in question.

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Sample Input 1 Copy

Copy

4
RRGB

Sample Output 1 Copy

Copy

1

Only the triplet $(1, 3, 4)(1, 3, 4)$ satisfies both conditions. The triplet $(2, 3, 4)(2, 3, 4)$ satisfies the first condition but not the second, so it does not count.

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Sample Input 2 Copy

Copy

39
RBRBGRBGGBBRRGBBRRRBGGBRBGBRBGBRBBBGBBB

Sample Output 2 Copy

Copy

1800

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define rep(i,n) for(int i=0;i<n;i++)
#define repr(i,n) for(int i=n-1;i>=0;i--)
const int N=2e5;
int a[4005],b[4005],c[4005];//若改为vector<int>a,b,c错误，vector不能达成a[i]用法

int main(){
int n,l=0,m=0,r=0;
ll ans=0;
string s;
cin>>n>>s;
rep(i,n){
if(s[i]==‘R‘)
    a[l++]=i+1;
if(s[i]==‘G‘)
    b[m++]=i+1;
if(s[i]==‘B‘)
    c[r++]=i+1;
}
for(int i=0;i<l;i++)
for(int j=0;j<m;j++){
    int sum=r;
    int a1=min(a[i],b[j]);
    int b1=max(a[i],b[j]);
    if(2*a1-b1-1>=0&&2*a1-b1-1<n&&s[2*a1-b1-1]==‘B‘)
        sum--;
    if(2*b1-a1-1>=0&&2*b1-a1-1<n&&s[2*b1-a1-1]==‘B‘)
        sum--;
    if((a1+b1)%2==0&&s[(a1+b1)/2-1]==‘B‘)
        sum--;
    ans+=sum;
    //cout<<ans<<endl;
}
cout<<ans<<endl;
return 0;
}