Largest Submatrix

http://acm.hdu.edu.cn/showproblem.php?pid=2870

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)

Problem Description

Now here is a matrix with letter
‘a‘,‘b‘,‘c‘,‘w‘,‘x‘,‘y‘,‘z‘ and you can change ‘w‘ to ‘a‘ or ‘b‘, change ‘x‘ to
‘b‘ or ‘c‘, change ‘y‘ to ‘a‘ or ‘c‘, and change ‘z‘ to ‘a‘, ‘b‘ or ‘c‘. After
you changed it, what‘s the largest submatrix with the same letters you can
make?

Input

The input contains multiple test cases. Each test case
begins with m and n (1 ≤ m, n ≤ 1000) on line. Then come the elements of a
matrix in row-major order on m lines each with n letters. The input ends once
EOF is met.

Output

For each test case, output one line containing the
number of elements of the largest submatrix of all same letters.

Sample Input

2 4

abcw

wxyz

Sample Output

3

Source

2009
Multi-University Training Contest 7 - Host by FZU

Recommend

gaojie   |   We have carefully selected several similar
problems for you:  2830 2577 2845 1069 1058

指定字母可以全部变为某指定字母

问相同字母组成的最大子矩阵

hdu 1505 加强版

#include<cstdio>
#include<cstring>
#include<algorithm>
#define N 1001
using namespace std;
int n,m,k,minn,ans;
char s[N+2][N+2],t[N+2][N+2];
int l[N],r[N];
int a[N],b[N];
int q[N],tmp[N],head,tail;
void change(char w,char x,char y,char z)
{
    for(int i=1;i<=n;i++)
     for(int j=1;j<=m;j++)
      if(s[i][j]==x || s[i][j]==y || s[i][j]==z) t[i][j]=w;
      else t[i][j]=s[i][j];
}
void monotonous(int *c,int *d)
{
    int h=1;
    while(h<=m && !c[h]) h++;
    if(h>m) return;
    q[0]=c[h]; tmp[0]=h;
    head=0; tail=1;
    for(int i=h+1;i<=m;i++)
    {
        if(!c[i]) while(head<tail) d[tmp[head++]]=i-1;
        else if(head==tail) q[tail]=c[i],tmp[tail++]=i;
        else
        {
            while(head<tail && c[i]<q[tail-1]) d[tmp[--tail]]=i-1;
            q[tail]=c[i];
            tmp[tail++]=i;
        }
    }
    while(head<tail) d[tmp[head++]]=tmp[tail-1];
}
void solve(char x)
{
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if(t[i][j]!=x) a[j]=b[m-j+1]=0;
            else
            {
                if(t[i][j]==t[i-1][j]) a[j]++,b[m-j+1]++;
                 else a[j]=b[m-j+1]=1;
            }
        }
        monotonous(a,r);
        monotonous(b,l);
        for(int j=1;j<=m;j++) tmp[j]=l[j];
        for(int j=1;j<=m;j++) l[m-j+1]=m-tmp[j]+1;
        for(int j=1;j<=m;j++) ans=max(ans,(r[j]-l[j]+1)*a[j]);
    }
}
int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        ans=0;
        for(int i=1;i<=n;i++) scanf("%s",s[i]+1);
        change(‘a‘,‘w‘,‘y‘,‘z‘); solve(‘a‘);
        change(‘b‘,‘w‘,‘x‘,‘z‘); solve(‘b‘);
        change(‘c‘,‘x‘,‘y‘,‘z‘); solve(‘c‘);
        printf("%d\n",ans);
    }
}