頭條筆試題 三桶水湊出指定體積水

試題

代碼
考慮從上一狀態轉換到下一狀態有三種方法：
1、往某個桶加水
2、倒掉某桶的水
3、將一個桶的水往另一個桶裏倒

使用寬度優先搜索：
1、一旦找到結果必然是最優結果，求解最少次數。
2、有助剪枝，當log中保存的狀態一旦已經嘗試過肯定無需繼續嘗試。

import java.util.*;

class Main{
    public static void main(String[] args){
        int[] bucket = new int[3];
        int[] water = new int[]{3, 5, 8};
        int target = 4;
        int step = 0;
        int[][] shift = new int[][]{
                {0,1},{0,2},
                {1,0},{1,2},
                {2,0},{2,1},
        };
        HashSet<String> log = new HashSet<>();
        Queue<int[]> queue = new LinkedList<>();
        queue.offer(bucket);

        while(!queue.isEmpty()){
            int size = queue.size();
            for(int q=0; q<size; q++){

                bucket = queue.poll();
//                System.out.println(Arrays.toString(bucket)+step);

				//終止
                if (bucket[2] == target || bucket[1] == target ||bucket[0] == target) {
                    System.out.println(step);
                    return;
                }

                String cur_str = Arrays.toString(bucket);
                //剪枝
                if(log.contains(cur_str)){
                    continue;
                }

                log.add(cur_str);

                int tmp;
                for(int i=0; i<3; i++){
                    //倒入水
                    if(bucket[i] < water[i]){
                        tmp = bucket[i];
                        bucket[i] = water[i];
                        queue.offer(bucket.clone());
                        bucket[i] = tmp;
                    }
                    //倒出水
                    if(bucket[i] != 0){
                        tmp = bucket[i];
                        bucket[i] = 0;
                        queue.offer(bucket.clone());
                        bucket[i] = tmp;
                    }
                }

				//轉移水
                int f, t, from, to;
                for(int[] ss : shift){
                    f = ss[0];
                    t = ss[1];
                    from = bucket[f];
                    to = bucket[t];
                    if(from == 0){
                        continue;
                    }
                    int cap = bucket[f] + bucket[t] - water[t];
                    if(cap <= 0){
                        bucket[f] = 0;
                        bucket[t] = from + to;
                    }else{
                        bucket[f] = cap;
                        bucket[t] = water[t];
                    }
                    queue.offer(bucket.clone());
                    bucket[f] = from;
                    bucket[t] = to;
                }
            }
            step++;

        }
        System.out.println(-1);
    }
}