hdu 6188 贪心

#include<bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:102400000,102400000")
#define rep(i,a,b) for (int i=a; i<=b; ++i)
#define per(i,b,a) for (int i=b; i>=a; --i)
#define mes(a,b)  memset(a,b,sizeof(a))
#define INF 0x3f3f3f3f
#define MP make_pair
#define PB push_back
#define fi  first
#define se  second
typedef long long ll;
const int N = 2000005;

int n, ai, vis[N], ans1, ans2;
bool is(int x)
{
    if(x>=1 && x<=n && vis[x]) return true;
    return false;
}
int main()
{
    while(~scanf("%d", &n))
    {
        mes(vis, 0);   ans1=ans2=0;
        rep(i,1,n)
        {
            scanf("%d", &ai);
            ++vis[ai];
        }
        rep(i,1,N-1)
        {
            if(is(i) && is(i-1) && is(i-2)) {
                ++ans2, --vis[i], --vis[i-1], --vis[i-2];
            }
            ans1 += vis[i]/2,  vis[i] %= 2;
        }
        printf("%d\n", ans1+ans2);
    }

    return 0;
}