USACO 1.5 Checker Challenge (位操作)

#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 allQueensPlacedState;int solution[14];int numOfSolutions;void printColumnsCanPlaceIn(int columnsCanPlaceIn){int i;for (i = size - 1; i >= 0; i--)printf("%d ", (columnsCanPlaceIn >> i) & 1 ? 1 : 0);printf("\n");}void placeQueen(int row, int columnState, int leftDiagonalState, int rightDiagonalState){if (columnState == allQueensPlacedState){numOfSolutions++;if (numOfSolutions < 4){int i;for (i = 1; i <= size; i++)printf("%d ", solution[i]);printf("\n");}}int columnsCanPlaceIn = allQueensPlacedState & ~(columnState | leftDiagonalState | rightDiagonalState);//printColumnsCanPlaceIn(columnsCanPlaceIn);while (columnsCanPlaceIn != 0){//取columnsCanPlaceIn最后边的1赋给columnToPlaceInint columnToPlaceIn;int i;for (i = 0; i < size; i++){if( ((1 << i) & columnsCanPlaceIn) != 0){columnToPlaceIn = 1 << i;if (numOfSolutions < 4)solution[row] = i + 1;break;}}columnsCanPlaceIn = columnsCanPlaceIn - columnToPlaceIn;placeQueen(row + 1, columnState + columnToPlaceIn, (leftDiagonalState + columnToPlaceIn) << 1, (rightDiagonalState + columnToPlaceIn) >> 1);}}int main(){#if DEBUGint 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);#endifscanf("%d", &size);allQueensPlacedState =  (1 << size) - 1;numOfSolutions = 0;placeQueen(1, 0, 0, 0);printf("%d\n", numOfSolutions);#if DEBUG}#endifreturn 0;}