Submission #173328

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Source Code Expand

import java.math.BigInteger;
import java.util.Scanner;


public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
				a[i] = sc.nextInt();
		}

		long cases = 0;
		int prev = Integer.MIN_VALUE;
		int prevCount = 0;
		for (int i = 0; i < n; i++) {
			if (a[i] != -1 && prevCount == 0) {
				prev = a[i];
//				prevCount = 0;
				continue;
			} else if (a[i] != -1 && prevCount != 0){
				cases += conbination(a[i] - prev + prevCount, prevCount);
				prev = a[i];
				prevCount = 0;
				continue;
			} else {
				prevCount++;
				continue;
			}
		}

		System.out.println(cases);
		
		sc.close();
	}
	
	static long conbination(int n, int r) {
		r = Math.min(n - r, r);

		BigInteger result = new BigInteger("1");
		for (int i = n; i >= n - r + 1; i--) {
			result = result.multiply(new BigInteger(Integer.toString(i)));
		}
		for (int i = 1; i <= r; i++) {
			result = result.divide(new BigInteger(Integer.toString(i)));
		}

		result = result.mod(new BigInteger(Integer.toString(1000000007)));

		if (result.equals(BigInteger.ONE)) {
			result = BigInteger.ZERO;
		}
		return result.longValue();
	}
}

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