# 第四十七周ARTS总结

# Algorithm

Spiral Matrix (opens new window)

0ms | 100.00% Run time
37.7MB | 5.21% Memory

public List<Integer> spiralOrder(int[][] matrix) {
    List<Integer> ans = new ArrayList<>();

    if (matrix.length == 0) {
        return ans;
    }

    int top = 0;
    int bottom = matrix.length - 1;
    int left = 0;
    int right = matrix[0].length - 1;

    // 一圈圈的输出
    while (top <= bottom && left <= right) {
        // 最后一圈为一行或者一列时
        if (top == bottom) {
            for (int i = left; i <= right; i++) {
                ans.add(matrix[top][i]);
            }
            break;
        }
        if (left == right) {
            for (int i = top; i <= bottom; i++) {
                ans.add(matrix[i][left]);
            }
            break;
        }

        // 上
        for (int i = left; i < right; i++) {
            ans.add(matrix[top][i]);
        }

        // 右
        for (int i = top; i < bottom; i++) {
            ans.add(matrix[i][right]);
        }

        // 下
        for (int i = right; i > left; i--) {
            ans.add(matrix[bottom][i]);
        }

        // 左
        for (int i = bottom; i > top; i--) {
            ans.add(matrix[i][left]);
        }

        top++;
        bottom--;
        left++;
        right--;
    }

    return ans;
}

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# Review

Our Journey from Genymotion to the Android Emulator (opens new window)

# Tip

可在RecyclerView.ViewHolder里通过getAdapterPosition()获取当前被点击条目的索引
RecyclerView.Adapter中的getItemViewType实现时，则onCreateViewHolder会被多次调用，因此会创建多个ViewHolder，即使ViewType相同也会被多次创建
<fragment>标签中可以用name属性指定布局
替换Fragment的步骤：
1. FragmentManager fragmentManager = getSupportFragmentManager();
2. FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
3. fragmentTransaction.replace(R.id.fragment_container, new RightFragment());
4. fragmentTransaction.commit();
通过fragmentTransaction.addToBackStack(null);可以将替换的Fragment加入到返回栈
Fragment的生命周期：
- onAttach()：当碎片和活动建立关联时调用
- onCreateView()：当为碎片创建布局时调用
- onActivityCreated()：与碎片相关联的活动创建完毕后调用
- onDestroyView()：当与碎片相关的布局被移除时调用
- onDetach()：当碎片与活动解除关联时调用

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# 第四十七周ARTS总结

# Algorithm

# Review

# Tip

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