hdu 6188 Duizi and Shunzi

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<string>
#include<algorithm>
#include<iostream>
#include<queue>
#include<map>
#include<cmath>
#include<set>
#include<stack>
#define ll long long
#define pb push_back
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)>(y)?(y):(x))
#define cls(name,x) memset(name,x,sizeof(name))
#define fs first
#define sc second
#define mp make_pair
#define L(x) (1<<x)
#define next Next
using namespace std;
const int inf=1e9+10;
const ll llinf=1e16+10;
const int maxn=1e6+10;
const int maxm=1e3+10;
const int mod=1e9+7;
int n;
int A[maxn];
int c[maxn];
int main()
{
    //freopen("in.txt","r",stdin);
    while(~scanf("%d",&n))
    {
        cls(c,0);
        for(int i=1;i<=n;i++)
        {
            scanf("%d",&A[i]);
            c[A[i]]++;
        }
        int ans=0;
        for(int i=1;i<=n;i++)
        {
            if(c[i]>=3)
            {
                if(c[i]%2==1)
                {
                    ans+=(c[i]-1)/2;
                    c[i]=1;
                }
                else
                {
                    ans+=(c[i]-2)/2;
                    c[i]=2;
                }
            }
        }
        //ci变为1或2
        for(int i=1;i<=n-2;i++)
        {
            if(c[i]==1&&c[i+1]==1&&c[i+2])
            {
                c[i]=c[i+1]=0;
                c[i+2]--;
                ans++;
            }
        }
        for(int i=1;i<=n;i++)
        {
            if(c[i]==2)
                ans++;
        }
        printf("%d\n",ans);
    }
    return 0;
}