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#include <iostream>
#include <sstream>
#include <utility>
#include <vector>
#include <stack>
#include <set>
using namespace std;
using matrix = vector<vector<int>>;
using pt = pair<int,int>;
//=====================================================================
struct connect
{
bool idir = true, jdir = true;
};
//=====================================================================
bool operator < ( const pt &p, const pt &q ) // Define ordering, so as to put pts in a set
{
if ( p.first < q.first ) return true;
if ( p.first == q.first && p.second < q.second ) return true;
return false;
}
//=====================================================================
int floodfill( int i1, int j1, int i2, int j2, const matrix &a, vector< vector<connect> > &c )
{
int rows = a.size(), cols = a[0].size();
int value1 = a[i1][j1], value2 = a[i2][j2];
set<pt> fill; fill.insert( { i1, j1 } ); fill.insert( { i2, j2 } );
stack<pt> stk; stk.push ( { i1, j1 } ); stk.push ( { i2, j2 } );
int area = 2;
// Standard floodfill; test s, n, w, e points and add to a stack
while ( !stk.empty() )
{
pt p = stk.top();
stk.pop();
int i = p.first, j = p.second;
int im = i - 1, ip = i + 1, jm = j - 1, jp = j + 1;
p = pt( im, j );
if ( im >= 0 && fill.find( p ) == fill.end() && ( a[im][j] == value1 || a[im][j] == value2 ) )
{
stk.push( p ); fill.insert( p );
area++;
}
p = pt( ip, j );
if ( ip < rows && fill.find( { ip, j } ) == fill.end() && ( a[ip][j] == value1 || a[ip][j] == value2 ) )
{
stk.push( p ); fill.insert( p );
area++;
}
p = pt( i, jm );
if ( jm >= 0 && fill.find( { i, jm } ) == fill.end() && ( a[i][jm] == value1 || a[i][jm] == value2 ) )
{
stk.push( p ); fill.insert( p );
area++;
}
p = pt( i, jp );
if ( jp < cols && fill.find( { i, jp } ) == fill.end() && ( a[i][jp] == value1 || a[i][jp] == value2 ) )
{
stk.push( p ); fill.insert( p );
area++;
}
}
// Turn off connectors so this fill won't be scanned again
for ( pt p : fill )
{
int i = p.first, j = p.second;
int im = i - 1, ip = i + 1, jm = j - 1, jp = j + 1;
if ( im >= 0 && ( a[im][j ] == value1 || a[im][j ] == value2 ) ) c[im][j ].idir = false;
if ( ip < rows && ( a[ip][j ] == value1 || a[ip][j ] == value2 ) ) c[i ][j ].idir = false;
if ( jm >= 0 && ( a[i ][jm] == value1 || a[i ][jm] == value2 ) ) c[i ][jm].jdir = false;
if ( jp < cols && ( a[i ][jp] == value1 || a[i ][jp] == value2 ) ) c[i ][j ].jdir = false;
}
return area;
}
//=====================================================================
int main()
{
istream &in2 = cin; // Use this for actual input
stringstream in( // Version for testing
"4 5 \n"
"1 1 2 3 1 \n"
"3 1 2 5 2 \n"
"5 2 1 5 6 \n"
"1 3 1 2 1 \n"
);
// Read data
int rows, cols;
in >> rows >> cols;
matrix a( rows, vector<int>( cols ) );
vector< vector<connect> > c( rows, vector<connect>( cols ) );
for ( int i = 0; i < rows; i++ )
{
for ( int j = 0; j < cols; j++ ) in >> a[i][j];
}
// Adjust connectors for equal adjacent values (indicator 0)
bool different = false;
int a0 = a[0][0];
for ( int i = 0; i < rows; i++ )
{
for ( int j = 0; j < cols; j++ )
{
int value = a[i][j];
if ( value != a0 ) different = true;
if ( i < rows - 1 && a[i+1][j] == value ) c[i][j].idir = false;
if ( j < cols - 1 && a[i][j+1] == value ) c[i][j].jdir = false;
}
}
if ( !different ) // Deal with the trivial case ... all equal!
{
cout << rows * cols << '\n';
return 0;
}
// Optimise fills; always start on an UNUSED, NON-EQUAL pair
int maxArea = 0;
for ( int i = 0; i < rows - 1; i++ )
{
for ( int j = 0; j < cols - 1; j++ )
{
if ( c[i][j].idir )
{
int area = floodfill( i, j, i + 1, j, a, c );
if ( area > maxArea ) maxArea = area;
}
if ( c[i][j].jdir )
{
int area = floodfill( i, j, i, j + 1, a, c );
if ( area > maxArea ) maxArea = area;
}
}
}
cout << maxArea << '\n';
}
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