程式設計也快樂: 兩隻水壺 C程式碼 搜尋版

搜。解釋都在程式碼的註釋裡。程式碼也可以在http://codepad.org/93Rptbfh上看

#include<stdio.h>
#define MAX_QUEUE 100000
#define TARGET 3
#define A_VOLUMN 5
#define B_VOLUMN 6
#define min(a,b) (a) < (b) ? (a) : (b)

struct state {
  int bottleA; /* Remained water in bottle A */
  int bottleB; /* Remained water in bottle B */
  int action;  /* How this state is achieved from its father state */
  int father;  /* Where this state is transfered from */
};

enum Action {
  FILL_A, /* Fill A with full water */
  FILL_B, /* Fill B with full water */
  A_TO_B, /* Pour the water from A to B */
  B_TO_A, /* Pour the water from B to A */
  POUR_A, /* Pour all the water from A to the pool to make it empty*/
  POUR_B, /* Pour all the water from B to the pool to make it empty*/
  NONE    /* NONE ACTION */
};

struct state queue[MAX_QUEUE]; /* The search Queue*/

int head; /* The head of the search queue */

int tail; /* The tail of the search queue */

int success = 0; /* Whether the search has succeed */

int flag; /* This will record the target position in the queue*/

short checked[A_VOLUMN + 1][B_VOLUMN + 1] = {0};

/**
 * Initialize the search queue, insert the first state
 */
void init() {
  head = 0;
  tail = 1;
  queue[0].bottleA = 0;
  queue[0].bottleB = 0;
  queue[0].father = 0;
  queue[0].action = NONE;
  checked[0][0] = 1;
}

void update(int a, int b, enum Action action) {
  /* If this state is checked, ignore it */
  if (checked[a][b])
    return;

  /* Record the state in the queue and check it */
  queue[tail].bottleA = a;
  queue[tail].bottleB = b;
  queue[tail].action = action;
  queue[tail].father = head;
  checked[a][b] = 1;

  /* If we have arrived at the target, record the tail for backtracing the result */
  if (a == TARGET || b == TARGET) {
    success = 1;
    flag = tail;
  }
  tail++;
}

void generateStates() {
  int transfered_water;

  /* Fullfill the bottle A */
  update(A_VOLUMN, queue[head].bottleB, FILL_A);

  /* Fullfill the bottle B */
  update(queue[head].bottleA, B_VOLUMN, FILL_B);

  /* Transfer water from A to B */
  transfered_water = min(queue[head].bottleA, B_VOLUMN - queue[head].bottleB);
  update(queue[head].bottleA - transfered_water, queue[head].bottleB + transfered_water, A_TO_B);

  /* Transfer water from B to A */
  transfered_water = min(queue[head].bottleB, A_VOLUMN - queue[head].bottleA);
  update(queue[head].bottleA + transfered_water, queue[head].bottleB - transfered_water, B_TO_A);

  /* Empty Bottle A */
  update(0, queue[head].bottleB, POUR_A);

  /* Empty Bottle B */
  update(queue[head].bottleA, 0, POUR_B);
}

void work() {
  while(!success && head != tail) {
    generateStates();
    head++;
  };
}

void backtraceResult(int pointer) {
  if (pointer == 0)
    return;
  else
    backtraceResult(queue[pointer].father);

  static char* actions[] = {"Fill A with full water from the pool -> ",
                            "Fill B with full water from the pool -> ",
                            "Pour the water from A to B           -> ",
                            "Pour the water from B to A           -> ",
                            "Empty bottle A                       -> ",
                            "Empty bottle B                       -> "};
  printf("%s A:%3d B:%3d\n", actions[queue[pointer].action], queue[pointer].bottleA, queue[pointer].bottleB);
}

void printResult() {
  if (!success) {
    printf("Cannot search out the result!\n");
    return;
  }
  /* Print the initial state */
  printf("Start with A: 0 B: 0\n");
  /* Backtrace to output all states leading to the solution */
  backtraceResult(flag);
  /* Print a success to indicate we achieved our goal */
  printf("Success!\n");
}

int main() {
  init();
  work();
  printResult();
  return 0;
}

結果：

Start with A: 0 B: 0
Fill A with full water from the pool ->  A:  5 B:  0
Pour the water from A to B           ->  A:  0 B:  5
Fill A with full water from the pool ->  A:  5 B:  5
Pour the water from A to B           ->  A:  4 B:  6
Empty bottle B                            ->  A:  4 B:  0
Pour the water from A to B           ->  A:  0 B:  4
Fill A with full water from the pool ->  A:  5 B:  4
Pour the water from A to B           ->  A:  3 B:  6
Success!