USACO 1.4 The Clocks (位操作+枚举+DFS)

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#USACO #The Clocks #位操作 #DFS #枚举

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本文深入探讨了在编程领域中应用复杂算法与数据结构的策略与实践，包括排序算法、动态规划、哈希算法等核心概念，旨在帮助开发者优化代码性能，解决实际问题。

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#include <stdio.h>
#define DEBUG 1
#define TESTCASES 9
#define INF (1 << 31 - 1)
#define CLOCKS 9
#define MOVES 9

int arrayOfMoves[MOVES + 1] = {0, 18911232, 19136512, 2363904, 16810048, 2134536, 262657, 36936, 73, 4617};
int set = 57521883;
int minTurns;
int finalSequence;

void turnDials(int state, int move, int numOfTurns, int sequence){
	if (numOfTurns > minTurns)
		return;

	if (move > MOVES){
		if (state == 0){
			if (numOfTurns < minTurns){
				minTurns = numOfTurns;
				finalSequence = sequence;
			} else if (sequence > finalSequence)
				finalSequence = sequence;
		}
		return;
	}

	int timesOfMove;
	for (timesOfMove = 0; timesOfMove <= 3; timesOfMove++){
		int newState = (state + arrayOfMoves[move] * timesOfMove) & set;
		//移位操作符优先级很低，注意加上各种括号
		int newSequence = sequence + (timesOfMove << (2 * (MOVES - move)));
		turnDials(newState, move + 1, numOfTurns + timesOfMove, newSequence);
	}
}

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
	
	int initialState = 0;
	int clock;
	for (clock = 1; clock <= CLOCKS; clock++){
		int colckState;
		scanf("%d", &colckState);
		initialState = (initialState << 3) + (colckState / 3 % 4);
	}

	minTurns = 28;
	finalSequence = 0;
	turnDials(initialState, 1, 0, 0);

	int move;
	for (move = 1; move <= MOVES; move++){
		int timesOfMove = ( finalSequence >> (2 * (MOVES - move) ) ) & 3;
		while (timesOfMove-- > 0){
			printf("%d%c", move, minTurns == 1 ? '\n' : ' ');
			minTurns--;
		}
	}

#if DEBUG
	}
#endif
	return 0;
}