题干：
Furik loves math lessons very much, so he doesn't attend them, unlike Rubik. But now Furik wants to get a good mark for math. For that Ms. Ivanova, his math teacher, gave him a new task. Furik solved the task immediately. Can you?
You are given a set of digits, your task is to find the maximum integer that you can make from these digits. The made number must be divisible by 2, 3, 5 without a residue. It is permitted to use not all digits from the set, it is forbidden to use leading zeroes.
Each digit is allowed to occur in the number the same number of times it occurs in the set.
Input
A single line contains a single integer n (1 ≤ n ≤ 100000) — the number of digits in the set. The second line contains n digits, the digits are separated by a single space.
Output
On a single line print the answer to the problem. If such number does not exist, then you should print -1.
Examples
Input
1
0
Output
0
Input
11
3 4 5 4 5 3 5 3 4 4 0
Output
5554443330
Input
8
3 2 5 1 5 2 2 3
Output
-1
Note
In the first sample there is only one number you can make — 0. In the second sample the sought number is 5554443330. In the third sample it is impossible to make the required number.
解题报告：
这题好恶心，明明不难的题，卡了半小时、、因为有前导零啊要特判。合适会出现前导零呢？在输入全为0时，或者有一个1剩下全是0这样的，或者两个2剩下全是0这样的。。并且不能读入完数据就特判刚开始写了if(a[n]==0) {puts("0");return 0;}，结果发现不对啊处理不了一个1剩下全是0这样的情况。然后改成if(sum == 0 || sum==1 || sum==2) { puts("0");return 0 ;}发现处理不了两个2剩下全是0的情况。。然后在每一个输出中都判断是否全是0这样、、、因为不判断就会出现前导零、、
AC代码：
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<queue>
#include<map>
#include<vector>
#include<set>
#include<string>
#include<cmath>
#include<cstring>
#define ll long long
#define pb push_back
#define pm make_pair
#define fi first
#define se second
using namespace std;
const int MAX = 2e5 + 5;
int a[MAX],sum,sum1,sum2;
int n;
bool bk[MAX];
int main()
{
cin>>n;
for(int i = 1; i<=n; i++) scanf("%d",a+i),sum+=a[i];
sort(a+1,a+n+1);
if(a[1] != 0) {
puts("-1");return 0 ;
}
if(sum == 0 || sum==1 || sum==2) {
puts("0");return 0 ;
}
if(sum%3 == 0) {
for(int i = n; i>=1; i--) printf("%d",a[i]);
return 0 ;
}
if(sum%3 == 1) {
int cnt1=0;
for(int i = 1; i<=n; i++) {
if(a[i]%3 == 1 && cnt1 != 1) {
bk[i]=1;cnt1++;continue;
}
sum1+=a[i];
}
if(sum1 == sum) {
int cnt2 = 0;
for(int i = 1; i<=n; i++) {
if(a[i]%3 == 2 && cnt2 != 2) {
bk[i]=1;cnt2++;continue;
}
sum2+=a[i];
}
if(cnt2 != 2) {
puts("-1");return 0 ;
}
else {
int flag = 0;
for(int i = n; i>=1; i--) {
if(bk[i] == 0) {
printf("%d",a[i]);if(a[i] == 0 && flag == 0) return 0 ;
flag=1;
}
}
return 0 ;
}
}
else {
int flag = 0;
for(int i = n; i>=1; i--) {
if(bk[i] == 0) {
printf("%d",a[i]);if(a[i] == 0 && flag == 0) return 0 ;
flag=1;
}
}
return 0 ;
}
}
//
if(sum%3 == 2) {
int cnt2=0;
for(int i = 1; i<=n; i++) {
if(a[i]%3 == 2 && cnt2 != 1) {
bk[i]=1;cnt2++;continue;
}
sum2+=a[i];
}
if(sum2 == sum) {
int cnt1=0;
for(int i = 1; i<=n; i++) {
if(a[i]%3 == 1 && cnt1 != 2) {
bk[i]=1;cnt1++;continue;
}
sum1+=a[i];
}
if(cnt1 != 2) {
puts("-1");return 0 ;
}
else {
int flag = 0;
for(int i = n; i>=1; i--) {
if(bk[i] == 0) {
printf("%d",a[i]);if(a[i] == 0 && flag == 0) return 0 ;
flag=1;
}
}
return 0 ;
}
}
else {
int flag=0;
for(int i = n; i>=1; i--) {
if(bk[i] == 0) {
printf("%d",a[i]);if(a[i] == 0 && flag == 0) return 0 ;
flag=1;
}
}
return 0 ;
}
}
return 0 ;
}
/*
11
3 9 9 6 4 3 6 4 9 6 0
Output
-1
Answer
999666330
*/
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