Codeforces Round #552 (Div. 3)B. Make Them Equal【水题】

思路：这题就是需要注意一下有坑点，要考虑有几位数字的不同情况。

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<iostream>
#include<algorithm>
using namespace std;
typedef long long ll;
#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1|1
const int maxn = 1e2 + 10;
const int inf = 0x3f3f3f3f;
int a[maxn];
int vis[maxn];
int num[maxn];
int main()
{
    int n;
    scanf("%d", &n);
    memset(vis, 0, sizeof(vis));
    for(int i = 0; i < n; ++i)
    {
        scanf("%d", &a[i]);
        vis[a[i]] = 1;
    }
    int cnt = 0;
    for(int i = 0; i < maxn; ++i)
    {
        if(vis[i] == 1)
            num[cnt++] = i;
    }
    int ans = -1;
    if(cnt > 3)
        ans = -1;
    else
    {
        if(cnt == 3)
        {
            if(num[2] - num[1] == num[1] - num[0])
                ans = num[2] - num[1];
        }
        else if(cnt == 2)
        {
            if((num[1] - num[0]) % 2 == 1)
                ans = num[1] - num[0];
            else
                ans = (num[1] - num[0])/2;
        }
        else if(cnt == 1)
        {
            ans = 0;
        }
        if(ans < 0)
            ans = -1;
    }
    cout << ans << endl;
    return 0;
}