Reorder(思维)

题目 题意：给定一个数组 a i a_i ai​和m，求是否能重排 a i a_i ai​，使得 ∑ i = 1 n ∑ j = i n a j j = m \sum_{i=1}^n\sum_{j=i}^n\frac{a_j}{j}=m ∑i=1n​∑j=in​jaj​​=m，这里的除法是非整除除法， 5 2 = 2.5 \frac{5}{2}=2.5 25​=2.5 思路： ∑ i = 1 n ∑ j = i n a j j = ∑ i = 1 n a i = m \sum_{i=1}^n\sum_{j=i}^n\frac{a_j}{j}=\sum_{i=1}^na_i=m ∑i=1n​∑j=in​jaj​​=∑i=1n​ai​=m

#include
using namespace std;
#define ll long long 
const int maxn = 1000010;

int a[maxn];

int main() {
	int t;
	scanf("%d", &t);
	while (t--) {
		int n, m;
		scanf("%d%d", &n, &m);
		ll sum = 0;
		for (int i = 0, x; i