# poj3276

Face The Right Way

 Time Limit: 2000MS Memory Limit: 65536K Total Submissions: 5121 Accepted: 2374

Description

Farmer John has arranged his N (1 ≤ N ≤ 5,000) cows in a row and many of them are facing forward, like good cows. Some of them are facing backward, though, and he needs them all to face forward to make his life perfect.

Fortunately, FJ recently bought an automatic cow turning machine. Since he purchased the discount model, it must be irrevocably preset to turn K (1 ≤ K ≤ N) cows at once, and it can only turn cows that are all standing next to each other in line. Each time the machine is used, it reverses the facing direction of a contiguous group of K cows in the line (one cannot use it on fewer than K cows, e.g., at the either end of the line of cows). Each cow remains in the same *location* as before, but ends up facing the *opposite direction*. A cow that starts out facing forward will be turned backward by the machine and vice-versa.

Because FJ must pick a single, never-changing value of K, please help him determine the minimum value of K that minimizes the number of operations required by the machine to make all the cows face forward. Also determine M, the minimum number of machine operations required to get all the cows facing forward using that value of K.

Input

Line 1: A single integer: N
Lines 2..N+1: Line i+1 contains a single character, F or B, indicating whether cow i is facing forward or backward.

Output

Line 1: Two space-separated integers: K and M

Sample Input

```7
B
B
F
B
F
B
B```

Sample Output

`3 3`

Hint

For K = 3, the machine must be operated three times: turn cows (1,2,3), (3,4,5), and finally (5,6,7)

Source

USACO 2007 March Gold  ac代码

```import java.util.Scanner;

public class Main{

/**
* @param args
*/
static int dir[]=new int[5000+2];
static int n;
static int f[]=new int[5000+2];
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner scan=new Scanner(System.in);
n=scan.nextInt();
scan.nextLine();
for(int i=0;i<n;i++){
String str=scan.nextLine();
if(str.equals("F")){
dir[i]=0;
}else{
dir[i]=1;
}
}
sovle();
}
private static void sovle() {
// TODO Auto-generated method stub
int M=n,K=1;
for(int k=1;k<=n;k++){
int m=calc(k);
if(m>0&&M>m){
M=m;
K=k;
}
}
System.out.println(K+" "+M);
}
private static int calc(int k) {
// TODO Auto-generated method stub
init();
int res=0;
int sum=0;
for(int i=0;i+k<=n;i++){
if((dir[i]+sum)%2!=0){
res++;
f[i]=1;
}
sum+=f[i];
if(i-k+1>=0){
sum-=f[i-k+1];
}
}
for(int i=n-k+1;i<n;i++){
if((dir[i]+sum)%2!=0){
return -1;
}
if(i-k+1>=0){
sum-=f[i-k+1];
}
}
return res;
}
private static void init() {
// TODO Auto-generated method stub
for(int i=0;i<n;i++){
f[i]=0;
}
}

}
```

## 【反转】POJ3276

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## poj3276 Face The Right Way

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## POJ3276 Face The Right Way 【尺取法】

Face The Right Way Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 2721   Accepted: 1246 Description Farmer John has arranged his N (1 ≤ N ≤ 5,000) cows in a row and many of them are facing forward, like good cows. Some of them are facin

## POJ3276——暴力——Fliptile

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## POJ3276 Face The Right Way 开关问题

①每个K从最左边进行考虑 ②f[i]=[i,i+k-1]是否进行反转:1代表是,0代表否 ③∑ (i)(i=i+1-K+1) f[j]=∑ (i-1)(i=i-K+1) f[j]+f[i]-f[i-K+1] 1 #include<cstdio> 2 #include<iostream> 3 #include<algorithm> 4 #include<queue> 5 #include<map> 6 #include<vector>

## 反转 开关问题 