URAL 1221 Malevich Strikes Back! (DP動態規劃 O(n^2) )

#include <stdio.h>
#define MAX_SIZE 101
#define MIN(x, y) ( (x) < (y) ? (x) : (y) )
int paper[MAX_SIZE][MAX_SIZE];
//存儲從左上left top 到右下 right bottom的掃描結果
int lt2rb[MAX_SIZE][MAX_SIZE];
int lb2rt[MAX_SIZE][MAX_SIZE];
int rt2lb[MAX_SIZE][MAX_SIZE];
int rb2lt[MAX_SIZE][MAX_SIZE];

int main(){
	
	int paperSize;
	while (scanf("%d", &paperSize) != EOF && paperSize != 0){
		int row, column;
		for (row = 1; row <= paperSize; row++)
			for (column = 1; column <= paperSize; column++)
				scanf("%d", &paper[row][column]);

		//先掃描四個邊沿
		int i;
		for (i = 1; i <= paperSize; i++){
			//上
			if (paper[1][i] == 0)
				lt2rb[1][i]= rt2lb[1][i] = 1;
			else
				lt2rb[1][i]= rt2lb[1][i] = 0;
			//下
			if (paper[paperSize][i] == 0)
				lb2rt[paperSize][i] = rb2lt[paperSize][i] = 1;
			else
				lb2rt[paperSize][i] = rb2lt[paperSize][i] = 0;
			//左
			if (paper[i][1] == 0)
				lt2rb[i][1] = lb2rt[i][1] = 1;
			else
				lt2rb[i][1] = lb2rt[i][1] = 0;
			//右
			if (paper[i][paperSize] == 0)
				rt2lb[i][paperSize]  = rb2lt[i][paperSize] = 1;
			else
				rt2lb[i][paperSize]  = rb2lt[i][paperSize] = 0;
		}

		int temp;

		//從左上角往右下角掃描
		for (row = 1; row <= paperSize; row++)
			for (column = 1; column <= paperSize; column++){
				if (paper[row][column] == 1)
					lt2rb[row][column] = 0;
				else {
					temp = MIN(lt2rb[row - 1][column], lt2rb[row][column - 1]);
					if (paper[row - temp][column - temp] == 1)
						//對角位置爲黑色
						lt2rb[row][column] = temp + 1;
					else 
						lt2rb[row][column] = 1;
				}
			}
		//從左下角往右上角掃描
		for (row = paperSize; row >= 1; row--)
			for (column = 1; column <= paperSize; column++){
				if (paper[row][column] == 1)
					lb2rt[row][column] = 0;
				else {
					temp = MIN(lb2rt[row + 1][column], lb2rt[row][column - 1]);
					if (paper[row + temp][column - temp] == 1)
						lb2rt[row][column] = temp + 1;
					else 
						lb2rt[row][column] = 1;
				}
			}
		//從右上角往左下角掃描
		for (row = 1; row <= paperSize; row++)
			for (column = paperSize; column >= 1; column--){
				if (paper[row][column] == 1)
					rt2lb[row][column] = 0;
				else {
					temp = MIN(rt2lb[row - 1][column], rt2lb[row][column + 1]);
					if (paper[row - temp][column + temp] == 1)
						rt2lb[row][column] = temp + 1;
					else 
						rt2lb[row][column] = 1;
				}
			}
		//從右下角往左上角掃描
		for (row = paperSize; row >= 1; row--)
			for (column = paperSize; column >= 1; column--){
				if (paper[row][column] == 1)
					rb2lt[row][column] = 0;
				else {
					temp = MIN(rb2lt[row + 1][column], rb2lt[row][column + 1]);
					if (paper[row + temp][column + temp] == 1)
						rb2lt[row][column] = temp + 1;
					else 
						rb2lt[row][column] = 1;
				}
			}

		int max = 0;
		for (row = 1; row <= paperSize; row++)
			for (column = 1; column <= paperSize; column++){
				temp = lt2rb[row][column];
				if (temp == lb2rt[row][column] && temp == rt2lb[row][column] && temp == rb2lt[row][column])
					if (temp > max)
						max = temp;
			}
		
		if (max > 1)
			printf("%d\n", (max << 1) - 1);
		else
			printf("No solution\n");
	}
	return 0;
}