Two progressions(CodeForces-125D)[鸽巢原理]

#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;
int n,arr[30010],book[30010];

bool judge(){
    int ps,gap;
    int t1=1,t2;
    while(t1<=n&&book[t1]) t1++;
    t2=t1+1;
    if(t1>n)
        return false;
    while(t2<=n&&book[t2]) t2++;
    if(t2>n)
        return true;
    gap=arr[t2]-arr[t1];
    ps=t2;
    for(int i=t2+1;i<=n;i++)
        if(!book[i]){
        if(arr[i]-arr[ps]==gap)
            ps=i;
        else
            return false;
        }
    return true;
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
        scanf("%d",&arr[i]); 
    if(n==2)
        printf("%d\n%d",arr[1],arr[2]);
    else {
        int x[3]={arr[2]-arr[1],arr[3]-arr[2],arr[3]-arr[1]};
        int flag=0;
        for(int i=0;i<3;i++){
            int st=4,tmp=arr[3];
            memset(book,0,sizeof(book));
            if(i==0){
                book[2]=book[1]=1;
                st=3;
                tmp=arr[2];
            }
            else if(i==1)
                book[2]=book[3]=1;
            else 
                book[1]=book[3]=1;
            for(int ii=st;ii<=n;ii++)
                if(arr[ii]==tmp+x[i]){
                    book[ii]=1;
                    tmp=arr[ii];
                }
            if(judge()){
                flag=1;
                break;
            }
            else {
                int p=n;
                while(!book[p])
                    p--;
                book[p]=0;
                if(judge()){
                    flag=1;
                    break;
                }
            }
        }
        if(flag){
            for(int i=1;i<=n;i++)
                if(book[i])
                    printf("%d ",arr[i]);
            printf("\n");
            for(int i=1;i<=n;i++)
                if(!book[i])
                    printf("%d ",arr[i]);
        }
        else printf("No solution");
    }
    return 0;
}