結果

問題 No.1011 Infinite Stairs
ユーザー 37zigen37zigen
提出日時 2020-03-20 22:15:59
言語 Java11
(openjdk 11.0.7)
結果
AC  
実行時間 148 ms / 2,000 ms
コード長 2,826 Byte
コンパイル時間 2,305 ms
使用メモリ 33,216 KB
最終ジャッジ日時 2020-06-05 11:21:44

テストケース

テストケース表示
入力 結果 実行時間
使用メモリ
testcase_00 AC 142 ms
33,204 KB
testcase_01 AC 143 ms
33,204 KB
testcase_02 AC 144 ms
33,200 KB
testcase_03 AC 147 ms
33,204 KB
testcase_04 AC 143 ms
33,204 KB
testcase_05 AC 146 ms
33,200 KB
testcase_06 AC 144 ms
33,204 KB
testcase_07 AC 147 ms
33,204 KB
testcase_08 AC 144 ms
33,204 KB
testcase_09 AC 143 ms
33,204 KB
testcase_10 AC 144 ms
33,204 KB
testcase_11 AC 146 ms
33,208 KB
testcase_12 AC 148 ms
33,208 KB
testcase_13 AC 148 ms
33,200 KB
testcase_14 AC 148 ms
33,208 KB
testcase_15 AC 141 ms
33,204 KB
testcase_16 AC 139 ms
33,208 KB
testcase_17 AC 135 ms
33,216 KB
testcase_18 AC 143 ms
33,204 KB
testcase_19 AC 141 ms
33,204 KB
testcase_20 AC 143 ms
33,204 KB
testcase_21 AC 139 ms
33,208 KB
testcase_22 AC 141 ms
33,200 KB
testcase_23 AC 141 ms
33,204 KB
testcase_24 AC 143 ms
33,204 KB
testcase_25 AC 140 ms
33,200 KB
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ソースコード

diff #
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.NoSuchElementException;

public class Main {
	public static void main(String[] args) throws FileNotFoundException {
		long t = System.currentTimeMillis();
		new Main().run();
		System.err.println(System.currentTimeMillis() - t);
	}
	
	Scanner sc = new Scanner();
	final long MOD=(long)1e9+7;
	
	long[] fac=new long[500000];
	long[] ifac=new long[500000];
	long[] inv=new long[500000];
	{
		fac[0]=fac[1]=ifac[0]=ifac[1]=inv[0]=inv[1]=1;
		for(int i=2;i<fac.length;++i) {
			fac[i]=i*fac[i-1]%MOD;
			inv[i]=MOD-inv[(int)(MOD%i)]*(MOD/i)%MOD;
			ifac[i]=inv[i]*ifac[i-1]%MOD;
		}
	}
	
	long comb(int n,int k) {
		if(k<0||n-k<0)return 0;
		return fac[n]*ifac[k]%MOD*ifac[n-k]%MOD;
	}
	
	void run() {
		int N=sc.nextInt();
		int d=sc.nextInt();
		int K=sc.nextInt();
		long ans=0;
		for(int i=0;i<=N;++i) {
			ans+=comb(N,i)*(i%2==0?1:-1)*comb(N+(K-N-d*i)-1,K-N-d*i)%MOD;
			ans%=MOD;
		}
		System.out.println((ans+MOD)%MOD);
	}
		
	class Scanner {
		private final InputStream in = System.in;
		private final byte[] buffer = new byte[1024];
		private int ptr = 0;
		private int buflen = 0;

		private boolean hasNextByte() {
			if (ptr < buflen) {
				return true;
			} else {
				ptr = 0;
				try {
					buflen = in.read(buffer);
				} catch (IOException e) {
					e.printStackTrace();
				}
				if (buflen <= 0) {
					return false;
				}
			}
			return true;
		}

		private int readByte() {
			if (hasNextByte())
				return buffer[ptr++];
			else
				return -1;
		}

		private boolean isPrintableChar(int c) {
			return 33 <= c && c <= 126;
		}

		private void skipUnprintable() {
			while (hasNextByte() && !isPrintableChar(buffer[ptr]))
				ptr++;
		}

		public boolean hasNext() {
			skipUnprintable();
			return hasNextByte();
		}

		public String next() {
			if (!hasNext())
				throw new NoSuchElementException();
			StringBuilder sb = new StringBuilder();
			int b = readByte();
			while (isPrintableChar(b)) {
				sb.appendCodePoint(b);
				b = readByte();
			}
			return sb.toString();
		}

		public long nextLong() {
			if (!hasNext())
				throw new NoSuchElementException();
			long n = 0;
			boolean minus = false;
			int b = readByte();
			if (b == '-') {
				minus = true;
				b = readByte();
			}
			if (b < '0' || '9' < b) {
				throw new NumberFormatException();
			}
			while (true) {
				if ('0' <= b && b <= '9') {
					n *= 10;
					n += b - '0';
				} else if (b == -1 || !isPrintableChar(b)) {
					return minus ? -n : n;
				} else {
					throw new NumberFormatException();
				}
				b = readByte();
			}
		}

		public int nextInt() {
			return (int) nextLong();
		}
	}

	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}
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