Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.
For example,
Given the following matrix:
[
[ 1, 2, 3 ],
[ 4, 5, 6 ],
[ 7, 8, 9 ]
]
You should return [1,2,3,6,9,8,7,4,5].
题意：转圈往里扫，边扫边放到集合里面。
java代码：
public List<Integer> spiralOrder(int[][] matrix) {
List<Integer> res = new ArrayList<Integer>();
if ( matrix == null || matrix.length == 0) {
return res;
}
int rowBegin = 0;
int rowEnd = matrix.length - 1;
int colBegin = 0;
int colEnd = matrix[0].length - 1;
while( rowBegin <= rowEnd && colBegin <= colEnd) {
//traverse right
for(int i=colBegin;i<=colEnd;i++)
res.add(matrix[rowBegin][i]);
rowBegin++;
//traverse down
for(int i=rowBegin;i<=rowEnd;i++)
res.add(matrix[i][colEnd]);
colEnd--;
//traverse left
if(rowBegin <= rowEnd) {
for(int i=colEnd;i>=colBegin;i--)
res.add(matrix[rowEnd][i]);
rowEnd--;
}
//traverse up
if(colBegin <= colEnd) {
for(int i=rowEnd;i>=rowBegin;i--)
res.add(matrix[i][colBegin]);
colBegin++;
}
}
return res;
}
