[二分 ST表] HihoCoder #1469 Challenge 27 福字

来源：互联网发布：豆瓣fm for mac 编辑：程序博客网时间：2024/06/09 16:04

这个只要枚举左上角然后二分最大值 xjb搞一下就好了

#include<cstdio>#include<cstdlib>#include<algorithm>using namespace std;inline char nc(){  static char buf[100000],*p1=buf,*p2=buf;  return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;}inline void read(int &x){  char c=nc(),b=1;  for (;!(c>='0' && c<='9');c=nc()) if (c=='-') b=-1;  for (x=0;c>='0' && c<='9';x=x*10+c-'0',c=nc()); x*=b;}const int N=1005;const int K=12;struct ST{    int st[N][K],Log[N];    inline void Pre(int *a,int n){      for (int i=2;i<=n;i++) Log[i]=Log[i>>1]+1;      for (int i=1;i<=n;i++) st[i][0]=a[i];      for (int k=1;k<K;k++)        for (int i=1;i<=n;i++)      {        st[i][k]=st[i][k-1];        if (i+(1<<(k-1))<=n)          st[i][k]=min(st[i][k],st[i+(1<<(k-1))][k-1]);      }    }    inline int Query(int l,int r){      int t=Log[r-l+1];      return min(st[l][t],st[r-(1<<t)+1][t]);    }  }B[N],C[N];inline bool check(int x,int y,int k){  return C[x].Query(y,y+k-1)>=k && B[y].Query(x,x+k-1)>=k;}int n;int a[N][N];int b[N][N],c[N][N];int main(){  freopen("t.in","r",stdin);  freopen("t.out","w",stdout);  read(n);  for (int i=1;i<=n;i++) for (int j=1;j<=n;j++) read(a[i][j]);  for (int i=1;i<=n;i++){    b[i][n]=1; int cnt=1;    for (int j=n-1;j;j--){      if (a[i][j]==a[i][j+1]-1)    cnt++;      else    cnt=1;      b[i][j]=cnt;    }  }  for (int i=1;i<=n;i++)    for (int j=1;j<i;j++) swap(b[i][j],b[j][i]);  for (int j=1;j<=n;j++){    c[n][j]=1; int cnt=1;    for (int i=n-1;i;i--){      if (a[i][j]==a[i+1][j]-1)    cnt++;      else    cnt=1;      c[i][j]=cnt;    }  }  int ans=0;  for (int i=1;i<=n;i++)    B[i].Pre(b[i],n),C[i].Pre(c[i],n);  for (int i=1;i<=n;i++)    for (int j=1;j<=n;j++){      int L=1,R=min(n-i+1,n-j+1)+1,MID;      while (L+1<R)    if (check(i,j,MID=(L+R)>>1))      L=MID;    else      R=MID;      ans=max(ans,L);    }  printf("%d\n",ans);  return 0;}

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