FESTIVAL 록 페스티벌 / algospot.com

문제링크 : https://algospot.com/judge/problem/read/FESTIVAL
제출링크 : https://algospot.com/judge/submission/detail/653190
자바 소스 : https://github.com/skysign/WSAPT/blob/master/algospot.com/FESTIVAL/src/Main.java

문제는 2가지 기법을 묻는 문제입니다.

• prefix sum 여기를 참고하세요 → https://skysign.tistory.com/171
• 평균의 구간이 band수에서 시작해서, N까지 증가합니다.

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Scanner;

/**
 * FESTIVAL 록 페스티벌 / algospot.com
 * 문제링크 : https://algospot.com/judge/problem/read/FESTIVAL
 * 제출링크 : https://algospot.com/judge/submission/detail/653190
 */
public class Main {
    public static void main(String[] args) throws IOException {
//        Scanner sc = new Scanner(System.in);
        Reader sc = new Reader();
        int T = sc.nextInt();

        for(int t=0; t<T; ++t) {
            int N = sc.nextInt();
            int band = sc.nextInt();
            int[] cs = new int[N+1];
            for(int n=1; n<=N; ++n) {
                cs[n] = sc.nextInt();
            }
            solve(N, band, cs);
        }
    }

    public static void solve(int N, int band, int[] cs) {
        int[] prefixSum = new int[N+1];

        for(int i=1; i<=N; ++i) {
            prefixSum[i] = cs[i] + prefixSum[i-1];
        }

        double mean = Integer.MAX_VALUE;
        for(int b=band; b<=N; ++b) {
            for(int i=1; i<=N-b+1; ++i) {
                int beg = i;
                int end = i+b-1;
                int sum = prefixSum[end] - prefixSum[beg-1];

                mean = Math.min(mean, (double)sum/(double)b);
            }
        }

        System.out.println(mean);
    }

    // https://www.geeksforgeeks.org/fast-io-in-java-in-competitive-programming/
    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String nextLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            }  while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }
}