【白书训练指南】（UVa10755）Garbage Heap

先po代码，之后把我那几个不太明了的知识点讲讲，巩固以下。三维的扫描线算法想要掌握还真是有一定的难度的。

代码

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#define FOR(i,s,t) for(int i=(s);i<=(t);++i)
using namespace std;
typedef long long ll;
const ll INF=1ll<<60;
const int maxn=25;
inline void expand(int i, int& b0, int& b1,int& b2)
{
    b0=i&1; i>>=1;
    b1=i&1; i>>=1;
    b2=i&1;
    return;
}
inline int sign(int b0,int b1,int b2)
{
    return (b0+b1+b2)%2?1:-1;
}
ll heap[maxn][maxn][maxn];
ll sum(int x1,int x2,int y1,int y2,int z1,int z2)
{
    int dx=x2-x1+1,dy=y2-y1+1,dz=z2-z1+1;
    ll s=0;
    for(int i=0;i!=8;++i)
    {
        int b0,b1,b2;
        expand(i,b0,b1,b2);
        s-=heap[x2-b0*dx][y2-b1*dy][z2-b2*dz]*sign(b0,b1,b2);
    }
    return s;
}
int main()
{
    int T; cin>>T;
    while(T--)
    {
        memset(heap,0,sizeof(heap));
        int a,b,c,b0,b1,b2;
        cin>>a>>b>>c;
        FOR(i,1,a) FOR(j,1,b) FOR(k,1,c) cin>>heap[i][j][k];
        FOR(i,1,a) FOR(j,1,b) FOR(k,1,c) FOR(p,1,7)
        {
            expand(p,b0,b1,b2);
            heap[i][j][k]+=heap[i-b0][j-b1][k-b2]*sign(b0,b1,b2);//?????
        }
        ll ans=-INF;
        FOR(x1,1,a) FOR(x2,x1,a) FOR(y1,1,b) FOR(y2,y1,b)
        {
            ll tmpM=0;
            FOR(z,1,c)
            {
                ll s=sum(x1,x2,y1,y2,1,z);
                ans=max(ans,s-tmpM);
                tmpM=min(tmpM,s);
            }
        }
        cout<<ans<<endl;
        if(T) cout<<endl;
    }
    return 0;
}