/**
* https://leetcode-cn.com/problems/spiral-matrix/
*/
public class _54_螺旋矩阵 {
public List<Integer> spiralOrder(int[][] matrix) {
if (matrix == null) return null;
List<Integer> res = new ArrayList<>();
if (matrix.length == 0) return res;

int top = 0;
int bottom = matrix.length - 1;
int left 
int right = matrix[0].length - 1;
while (top <= bottom && left <= right) {
// left top -> right top
for (int i = left; i <= right; i++) {
res.add(matrix[top][i]);
}
top++;

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

// 奇数行、偶数列的时候有问题
if (top > bottom || left > right) break;

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

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

return res;
}
}