Codeforces Round #577 (Div. 2)
You are given an array a1,a2,…,an.
In one operation you can choose two elements ai and aj (i≠j) and decrease each of them by one.
You need to check whether it is possible to make all the elements equal to zero or not.
Input
The first line contains a single integer n (2≤n≤105) — the size of the array.
The second line contains n integers a1,a2,…,an (1≤ai≤109) — the elements of the array.
Output
Print "YES" if it is possible to make all elements zero, otherwise print "NO".
Examples
input
4
1 1 2 2
output
YES
input
6
1 2 3 4 5 6
output
NO
Note
In the first example, you can make all elements equal to zero in 3 operations:
- Decrease a1 and a2,
- Decrease a3 and a4,
- Decrease a3 and a4
In the second example, one can show that it is impossible to make all elements equal to zero.
题意：题目意思是给你n个数，你可以进行任意次操作：对序列里的两个数都减一，
问你最后能不能把序列n个数都变成0。
思路：显然如果n个数的总和是奇数，肯定不能把n个数都变0。
还有就是序列中最大的数比总和的一半还大，即最大值的两倍大于总和，
这也是不行的，因为就算你拿另外n-1个数对最大值去操作，最后这个数还是不会变0，
然后其他情况都是可以的。
1 #include<iostream>
2 #include<cstdio>
3 #include<cstring>
4 #include<cmath>
5 #include<algorithm>
6 #include<map>
7 #include<set>
8 #include<vector>
9 #include<queue>
10 #include<list>
11 //#include<unordered_map>
12 #include<stack>
13 using namespace std;
14 #define ll long long
15 const int mod=1e9+7;
16 const int inf=1e9+7;
17
18 const int maxn=1e5+10;
19
20 int main()
21 {
22 ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
23
24 int n;
25 cin>>n;
26 ll int num;
27 ll int maxx=-1,sum;
28 for(int i=0;i<n;i++)
29 {
30 cin>>num;
31 sum+=num;
32
33 if(num>maxx)
34 maxx=num;
35 }
36
37 if(sum&1||maxx*2>sum)
38 return cout<<"NO"<<endl,0;
39 else
40 return cout<<"YES"<<endl,0;
41
42 return 0;
43 }