POJ 3378 Crazy Thairs（树状数组+DP）

#include <cstdio>
#include <algorithm>
#include <cstring> 
using namespace std;
typedef long long LL;
const int N=50010;
int n,a[N];
int disc[N];
struct Num{
    short len,a[20];
    Num(){len=1;for(int i=0;i<20;i++)a[i]=0;}
    Num operator+(Num b){
        Num c;
        c.len=len>b.len?len:b.len;c.len+=2;
        for(int i=1;i<=c.len;i++)c.a[i]=a[i]+b.a[i];
        for(int i=1;i<=c.len;i++)c.a[i+1]+=c.a[i]/10000,c.a[i]%=10000;
        while(c.len>1&&!c.a[c.len])c.len--;
        return c;
    }void print(){for(int i=len;i;i--)printf(i==len?"%d":"%04d",a[i]);puts("");}
}c[5][N];
void modify(int k,int x,Num val){while(x<=n)c[k][x]=c[k][x]+val,x+=x&-x;}
Num query(int k,int x){Num s;while(x>0)s=s+c[k][x],x-=x&-x;return s;}
int remark(int x){
    int l=1,r=n;
    while(l<=r){
        int mid=(l+r)>>1;
        if(disc[mid]<x)l=mid+1;
        else if(disc[mid]==x)return mid;
        else r=mid-1;
    }
}
int main(){
    while(~scanf("%d",&n)){
        Num one; one.a[1]=1;
        memset(c,0,sizeof(c));
        for(int i=1;i<=n;i++)scanf("%d",&a[i]),disc[i]=a[i];
        sort(disc+1,disc+n+1);
        for(int i=1;i<=n;i++){
            a[i]=remark(a[i]);
            modify(0,a[i],one);
            for(int k=1;k<5;k++){
                Num x=query(k-1,a[i]-1);
                modify(k,a[i],x);
            }
        }query(4,n).print();
    }return 0;
}