预处理

int a[n+1] = {0};
int cache[n+1] = {0};
for(int i = 1;i<=n;i++){
	cin >> a[i];
	cache[i] = a[i] + cache[i-1];
}

计算

if(j-i >= 0 && cache[j] - cache[j-i] <= m && cache[j] - cache[j-i] > 0){