CodeForces 525C Ilya and Sticks 贪心

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#include <iostream>
#include <cstdio>
#include <cstring> 
#include <algorithm>
typedef long long ll;
using namespace std;
const int M = 1e5+5;
int n;
int a[M];
int b[M];
bool cmp( int a, int b )  {   //从大到小排序
    return a > b;
}
int main()
{
    while( ~scanf("%d", &n ) )  {
        memset( b, 0, sizeof(b) );
        for( int i=0; i<n; i++ )
            scanf("%d", a+i);
        sort( a, a+n, cmp );
        int cnt = 0;
        for( int i=0; i<n-1; i++ )  {
            if( a[i]-a[i+1] <= 1 )  {
                b[cnt++] = a[i+1];
                i++;
            }
        }
        ll sum = 0;
        for( int i=0; i<cnt-cnt%2; i+=2 )  {
            sum += (ll)b[i]*(ll)b[i+1];
        }
        printf("%I64d\n", sum );
    }
    return 0;
}