BZOJ 1567: [JSOI2008]Blue Mary的战役地图

曾经终败给现在 2021-10-19 04:42 208阅读 0赞

[传送门][Link 1]

考虑二分答案暴力 $n^4$ 枚举两个矩形右下角，如果能做到 $O(1)$ 判断那么复杂度就可行

那么容易想到二维哈希，然后直接搞就好了...

二维哈希怎么做还是看代码吧...

#include<iostream>
    #include<cstdio>
    #include<algorithm>
    #include<cstring>
    #include<cmath>
    using namespace std;
    typedef unsigned long long ull;
    inline int read()
    {
        int x=0,f=1; char ch=getchar();
        while(ch<'0'||ch>'9') { if(ch=='-') f=-1; ch=getchar(); }
        while(ch>='0'&&ch<='9') { x=(x<<1)+(x<<3)+(ch^48); ch=getchar(); }
        return x*f;
    }
    const int N=57,base1=9924353,base2=1e9+7;
    int n,ans;
    ull ha1[N][N],ha2[N][N],hb1[N][N],hb2[N][N],fac1[N],fac2[N];
    inline ull get_h(int x,int y,int l,bool flag)
    {
        if(flag) return ha2[x][y]-ha2[x][y-l]*fac1[l]-ha2[x-l][y]*fac2[l]+ha2[x-l][y-l]*fac1[l]*fac2[l];
        return hb2[x][y]-hb2[x][y-l]*fac1[l]-hb2[x-l][y]*fac2[l]+hb2[x-l][y-l]*fac1[l]*fac2[l];
    }
    inline bool check(int p)
    {
        for(int i=p;i<=n;i++)
            for(int j=p;j<=n;j++)
                for(int k=p;k<=n;k++)
                    for(int l=p;l<=n;l++)
                        if(get_h(i,j,p,1)==get_h(k,l,p,0)) return 1;
        return 0;
    }
    int main()
    {
        n=read();
        fac1[0]=fac2[0]=1; for(int i=1;i<=n;i++) fac1[i]=fac1[i-1]*base1,fac2[i]=fac2[i-1]*base2;
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
                ha1[i][j]=ha1[i][j-1]*base1+read();
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
                hb1[i][j]=hb1[i][j-1]*base1+read();
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
            {
                ha2[i][j]=ha2[i-1][j]*base2+ha1[i][j],
                hb2[i][j]=hb2[i-1][j]*base2+hb1[i][j];
            }
        int L=1,R=n;
        while(L<=R)
        {
            int mid=L+R>>1;
            if(check(mid)) L=mid+1,ans=mid;
            else R=mid-1;
        }
        printf("%d\n",ans);
        return 0;
    }

转载于:https://www.cnblogs.com/LLTYYC/p/11349639.html

[Link 1]: https://www.lydsy.com/JudgeOnline/problem.php?id=1567