AcWing 4644. 求和 java
原题链接
简单
作者:
zwj_123
,
2024-04-11 17:00:35
,
所有人可见
,
阅读 1
java前缀和
import java.io.*;
import java.util.*;
public class Main {
public static void main(String []args){
Scanner cin = new Scanner(System.in);
long n = cin.nextLong();
long[] a = new long[(int)(n + 1)];
long[] sum = new long[(int)(n + 1)];
sum[0] = 0;
for(int i = 1;i <= n;i++){
a[i] = cin.nextLong();
sum[i] = sum[i-1] + a[i];
}
long total = sum[(int)(n)];
long s = 0;
for(int i = 1;i <= n;i++){
s += a[i] * (total - sum[i]);
}
System.out.println(s);
}
}