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emailed 2008-05-16 09:06:23

http://acm.tju.edu.cn/toj/showp2949.html

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可口可乐 2008-05-17

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优化了一下，速度提高很多
364596 2008-05-17 01:25:38 Accepted 2949 C++ 1.3K 0'01.25" 1212K brucesea



#include <iostream>

using namespace std;



#define N 301

bool matrix[N][N];



int nr, nc;



bool good(int i1, int j1, int size)

{

	if ( (i1<0) || (j1<0) || (i1+size-1>=nr) || (j1+size-1>=nc) ) return false;



	for (int k = 0; k < size; k++) {

		if (matrix[i1][j1+k] != matrix[i1+size-1][j1+size-k-1]) return false;

		if (matrix[i1+k][j1] != matrix[i1+size-k-1][j1+size-1]) return false;

	}



	return true;

}



int get()

{

	int ms = -1;

	for (int i = 0; i < nr; i++) {

		for (int j = 0; j < nc; j++) {

			if (ms != -1) {

				int k = ms/2;

				if (!good(i-k, j-k, 2*k+1)) continue;

			}

			for (int k = 1; ; k++) {

				if (good(i-k, j-k, 2*k+1)) ms = max(ms, 2*k+1);

				else break;

			}

		}

	}



	for (int i = 0; i < nr; i++) {

		for (int j = 0; j < nc; j++) {

			if (ms != -1) {

				int k = ms/2;

				if (!good(i-k, j-k, 2*k+2)) continue;

			}

			for (int k = 0; ; k++) {

				if (good(i-k, j-k, 2*k+2)) ms=max(ms, 2*k+2);

				else break;

			}

		}

	}



	return ms;

}



int main()

{

	char pstr[N];

	cin >> nr >> nc;

	cin.getline(pstr, N);



	for (int i = 0; i < nr; i++) {

		cin.getline(pstr, N);

		for (int j = 0; j < nc; j++) {

			matrix[i][j] = (pstr[j] == '1') ? true : false;

		}

	}



	cout << get() << endl;

	return 0;

}

可口可乐 2008-05-16

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以某一个点(i,j)作为中心，
边长逐渐递增，看所围的边是否满足条件，
满足边长就继续增加，
不满足就退出这个点，看下一个点



#include <iostream>

using namespace std;



bool matrix[400][400];

int nr, nc;



bool good(int i1, int j1, int size)

{

	for (int k = 0; k < size; k++) {

		if (matrix[i1][j1+k] != matrix[i1+size-1][j1+size-k-1]) return false;

		if (matrix[i1+k][j1] != matrix[i1+size-k-1][j1+size-1]) return false;

	}



	return true;

}



int get()

{

	int ms = -1;

	for (int i = 0; i < nr; i++) {

		for (int j = 0; j < nc; j++) {

			for (int k = 1; ((i>=k)&&(j>=k)&&(i+k<nr)&&(j+k<nc)); k++) {

				if (good(i-k, j-k, 2*k+1)) ms = max(ms, 2*k+1);

				else break;

			}

		}

	}



	for (int i = 0; i < nr-1; i++) {

		for (int j = 0; j < nc-1; j++) {

			for (int k = 0; ((i>=k)&&(j>=k)&&(i+k+1<nr)&&(j+k+1<nc)); k++) {

				if (good(i-k, j-k, 2*k+2)) ms=max(ms, 2*k+2);

				else break;

			}

		}

	}



	return ms;

}



int main()

{

	char pstr[400];

	cin >> nr >> nc;

	cin.getline(pstr, 400);



	for (int i = 0; i < nr; i++) {

		cin.getline(pstr, 400);

		for (int j = 0; j < nc; j++) {

			matrix[i][j] = (pstr[j] == '1') ? true : false;

		}

	}



	cout << get() << endl;

	return 0;

}