【SCU】Carries

#include<bits/stdc++.h>using namespace std;long long carries;const int MAXN=100010;int a[MAXN],b[MAXN];int main(void){    int n;    while(~scanf("%d",&n))    {        carries=0;        for(int i = 0; i < n; ++i)        {            scanf("%d",&a[i]);        }        int tmp=1;        for(int i = 1; i <= 9; ++i)        {            tmp*=10;            for(int j = 0; j < n; ++j)            {                b[j] = a[j]%tmp;            }            sort(b,b+n);            int left=n;            for(int j = 0; j < n; ++j)            {                while(left && b[j]+b[left-1]>=tmp)                    --left;                if(left<=j)                    carries+=(n-left-1);    //去掉b[j]                else                    carries+=(n-left);            }        }        carries/=2;        printf("%lld\n",carries);    }    return 0;}