LeetCode 31.水壶问题 数学方法与广度遍历

public boolean canMeasureWater(int x, int y, int z) {
           if(x+y<z){
                return false;
            }
            if(x == 0 || y == 0){
                return z==0 || x+y==z;
            }
            return z % gcb(x,y) == 0;
        }
        int gcb(int m, int n) {  
                if (m < n) {// 保证m>n,若m<n,则进行数据交换  
                    int temp = m;  
                    m = n;  
                    n = temp;  
                }  
                if (m % n == 0) {// 若余数为0,返回最大公约数  
                    return n;  
                } else { // 否则,进行递归,把n赋给m,把余数赋给n  
                    return gcb(n, m % n);  
                } 

        }

public boolean canMeasureWater(int x, int y, int z) {
   
        if (z > x + y) return false;
        if (x == z || y == z || x + y == z) return true;

        // 保存搜索过的情况，防止无止境的搜索下去
        Set<List<Integer>> set = new HashSet<>();

        // 保存每次操作后，x，y中剩余的水的容量
        LinkedList<List<Integer>> res = new LinkedList<>();

        // 初始时，x y中均没有水
        List<Integer> list = Arrays.asList(0, 0);
        set.add(list);
        res.add(list);

        while (!res.isEmpty()) {
            List<Integer> poll = res.poll();
            int remain_x = poll.get(0);
            int remain_y = poll.get(1);
            if (remain_x == z || remain_y == z || remain_x + remain_y == z) {
                return true;
            }

            // 给x加满水
            List<Integer> p1 = Arrays.asList(x, remain_y);
            if (!set.contains(p1)) {
                set.add(p1);
                res.add(p1);
            }

            // 给y加满水
            List<Integer> p2 = Arrays.asList(remain_x, y);
            if (!set.contains(p2)) {
                set.add(p2);
                res.add(p2);
            }


            // 清空x的水
            List<Integer> p3 = Arrays.asList(0, remain_y);
            if (!set.contains(p3)) {
                set.add(p3);
                res.add(p3);
            }

            // 清空y的水
            List<Integer> p4 = Arrays.asList(remain_x, 0);
            if (!set.contains(p4)) {
                set.add(p4);
                res.add(p4);
            }

            // x向y倒水
            int tmp_x = (remain_x + remain_y) <= y ? 0 : remain_x + remain_y - y;
            int tmp_y = (remain_x + remain_y) < y ? remain_x + remain_y : y;
            List<Integer> p5 = Arrays.asList(tmp_x, tmp_y);
            if (!set.contains(p5)) {
                set.add(p5);
                res.add(p5);
            }


            // y向x倒水
            tmp_y = (remain_x + remain_y) <= x ? 0 : remain_x + remain_y - x;
            tmp_x = (remain_x + remain_y) < x ? remain_x + remain_y : x;
            List<Integer> p6 = Arrays.asList(tmp_x, tmp_y);
            if (!set.contains(p6)) {
                set.add(p6);
                res.add(p6);
            }

        }

        return false;
    }
参考自：LeetCode用户yw-git