USACO 1.5 Checker Challenge (DFS + 剪枝)

#include <stdio.h>
#define DEBUG 1
#define TESTCASES 8
#define IN(x)  ( (x) >= 1 && (x) <= size ? 1 : 0 )
#define WITHIN(x, y) ( IN(x) && IN(y) ? 1 : 0 )
int size;
int sizeIsEven;
int halfSize;
int conflict[14][14];
int solution[14];
int numOfSolutions;
//剪枝：对角线冲突只要标记左下和右下两个方向
int directionArray[2][2] = {{1, 1}, {1, -1}};

void printConflict(){
	int i, j;
	for (i = 1; i <= size; i++)
		for (j = 1; j <= size; j++)
			printf("%d%c", conflict[i][j], j == size ? '\n' : ' ');
	printf("\n");
}

void setConflict(int row, int column, int flag){
	int i;
 	for (i = 1; i <= size; i++)
		conflict[i][column] += flag;
	int directionIndex;
	for (directionIndex = 0; directionIndex < 2; directionIndex++){
		int deltaX = directionArray[directionIndex][0];
		int deltaY = directionArray[directionIndex][1];
		int x = row + deltaX;
		int y = column + deltaY;
		while ( WITHIN(x, y) ){
			conflict[x][y] += flag;
			x += deltaX;
		    y += deltaY;
		}
	}
}

void placeQueen(int row, int sum){
	//printConflict();
	if (row == size){
		//剪枝:最后一行放棋子的列号可以算出来
		int temp = (1 + size) * size / 2 - sum;
		if (conflict[size][temp] == 0){
			solution[size] = temp;
			if (++numOfSolutions < 4){
				int i;
				for (i = 1; i <= size; i++)
					printf("%d ", solution[i]);
				printf("\n");
			}
		}
		return;
	}
	int column;
	for (column = 1; column <= size; column++){
		//剪枝：size为偶数时对称优化，size为奇数时怎么优化呢？
		if ( row == 1 && sizeIsEven && column  ==  halfSize + 1 && numOfSolutions >= 3){
			numOfSolutions *= 2;
			return;
		}
		if (conflict[row][column] == 0){
			solution[row] = column;
			setConflict(row, column, 1);
			placeQueen(row + 1, sum + column);
			setConflict(row, column, -1);

		}
	}
}

int main(){
#if DEBUG
	int testCase;
	for (testCase = 1; testCase <= TESTCASES; testCase++){
		char inputFileName[20] = "inputx.txt";
		inputFileName[5] = '1' +  (testCase - 1);
		freopen(inputFileName, "r", stdin);
		printf("\n#%d\n", testCase);
#endif

	scanf("%d", &size);
	halfSize = size >> 1;
	sizeIsEven = !(size & 1);

	numOfSolutions = 0;
	placeQueen(1, 0);
	printf("%d\n", numOfSolutions);

#if DEBUG
	}
#endif
	return 0;
}