描述
Three friends gathered to play a few games of chess together.
In every game, two of them play against each other. The winner gets 2 points while the loser gets 0, and in case of a draw, both players get 1 point each. Note that the same pair of players could have played any non-negative number of times (possibly zero). It is also possible that no games were played at all.
You've been told that their scores after all the games were played were p1, p2 and p3. Additionally, it is guaranteed that p1≤p2≤p3 holds.
Find the maximum number of draws that could have happened and print it. If there isn't any way to obtain p1, p2 and p3 as a result of a non-negative number of games between the three players, print −1 instead.
输入描述
Each test contains multiple test cases. The first line contains the number of test cases t (1≤t≤500). The description of the test cases follows.
The first line of each test case contains three integers p1, p2 and p3 (0≤p1≤p2≤p3≤30) — the scores of the three players, sorted non-decreasingly.
输出描述
For each testcase, print one number — the maximum possible number of draws that could've happened, or −1 if the scores aren't consistent with any valid set of games and results.
用例输入 1
7 0 0 0 0 1 1 1 1 1 1 1 2 3 3 3 3 4 5 1 1 10
用例输出 1
0 1 -1 2 -1 6 2
提示
In the first example, no games were played at all, so no draws could occur either.
For the second example, exactly one game occurred between the second and the third player and it ended in draw, so the answer is 1.
It's easy to see that there's no set of games achieving the scores in third example, so the answer for it is −1.
翻译：
描述
三个朋友聚在一起下了几盘棋。
在每场比赛中，他们中的两个人相互对抗。获胜者将获得2积分，而失败者获得0，如果出现平局，双方都会得到1点每个。请注意，同一对玩家可以玩任何非负数（可能为零）。也有可能根本没有玩任何游戏。
你被告知，他们在所有比赛结束后的得分是p1,p2和p3.此外，还保证p1≤p2≤p3保持。
找到可能发生的最大抽奖次数并打印出来。如果没有任何方法可以获得p1,p2和p3由于三名玩家之间的游戏数不为负数，请打印−1相反。
输入描述
每个测试都包含多个测试用例。第一行包含测试用例的数量t (1≤吨≤500).测试用例的描述如下。
每个测试用例的第一行包含三个整数p1,p2和p3 (0≤p1≤p2≤p3≤30） — 三名玩家的分数，不递减排序。
输出描述
对于每个测试用例，打印一个数字 — 可能发生的最大绘制次数，或者−1如果分数与任何一组有效的游戏和结果不一致。
用例输入 1
7
0 0 0
0 1 1
1 1 1
1 1 2
3 3 3
3 4 5
1 1 10 用例输出 1
0
1
-1
2
-1
6
2 提示
在第一个示例中，根本没有进行任何游戏，因此也不会发生平局。
对于第二个例子，第二位和第三位玩家之间恰好发生了一场比赛，并以平局告终，所以答案是1.
不难看出，在第三个例子中，没有一组游戏能达到分数，所以答案是−1.
解题思路：
1. 当平局时每人加1分，也就是本来赢得2分平分了，所以无论怎么打，只要有答案总分数就是偶数
2.因为要计算平局最大数，所以就将最大的两个-1，直到减不了为止
c++ 代码如下：
#include <bits/stdc++.h>using namespace std;int main()
{int n;cin >> n;while(n--){int res = 0;int a,b,c;cin >> a >> b >> c;int sum = a + b + c;if(sum%2 != 0){cout << -1 << endl;}else{//初始化setmultiset<int> s;s.insert(a);s.insert(b);s.insert(c);//初始化循环auto t1 = --s.end();auto t2 = --s.end();--t2;int num1 = *t1;int num2 = *t2;while(num2 >=1 && num1 >= 1){//更改元素--num1;--num2;s.erase(--s.end());s.erase(--s.end());s.insert(num1);s.insert(num2);//结果计数++res;//更新数据t1 = --s.end();t2 = --s.end();--t2;num1 = *t1;num2 = *t2;}cout << res << endl;}}
}-锁和事务语句)
