Educational Codeforces Round 34 (Rated for Div. 2) D - Almost Difference

参考：http://blog.youkuaiyun.com/kamiyoru/article/details/78791923

当读入第k个数字的时候：
ans′=∑k−1i=1(numberk−nubmeri)=(k−1)numberk−∑k−1i=1nubmeri
当然这不是实际的答案，因为差值为1及以内的数是不必加到答案上的；
所以
ans=ans′−countnumberk−1+countnumberk+1

include <cstdio>
#include <map>
using namespace std;
map<int,int> cnt;//计数器
int main(){
    int n;long double ans=0,sum=0,num;scanf("%d",&n);
    for(int i=0;i<n;i++){
        scanf("%Lf",&num);
        ans+=num*i-sum+cnt[(int)num+1]-cnt[(int)num-1];
        sum+=num;
        cnt[(int)num]++;
    }
    printf("%.0Lf",ans+0.000000001);
}