题解 | 大整数哈希

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

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scanner=new Scanner(System.in);
		int n=scanner.nextInt();
		HashMap<BigInteger, BigInteger> map=new HashMap<>();
		BigInteger sum=new BigInteger("0");
		BigInteger a=new BigInteger("2");
		a=a.pow(64);
		for (long i = 1; i <= n; i++) {
			BigInteger x=new BigInteger(scanner.next());
			BigInteger y=new BigInteger(scanner.next());
			sum=sum.add(map.getOrDefault(x, new BigInteger("0")).multiply(new BigInteger(""+i)));
			map.put(x, y);
		}
		System.out.println(sum.mod(a));
		

	}

}

这道题按照题意模拟就行，我们需要创建一个sum来装最后的结果，要注意，BigInteger的求模使用的是mod，这个我之前不知道