Spiral Matrix

Author: fishercoder1534

README.md

@@ -205,6 +205,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |60|[Permutation Sequence](https://leetcode.com/problems/permutation-sequence/)|[Solution](../../blob/master/src/stevesun/algorithms/PermutationSequence.java)|?|?|Medium|
 |58|[Length of Last Word](https://leetcode.com/problems/length-of-last-word/)|[Solution](../../blob/master/src/stevesun/algorithms/LengthofLastWord.java)|O(n)|O(1)|Easy|
 |56|[Merge Intervals](https://leetcode.com/problems/merge-intervals/)|[Solution](../../blob/master/src/stevesun/algorithms/MergeIntervals.java)|O(n*logn)|O(1)|Hard|
+|54|[Spiral Matrix](https://leetcode.com/problems/spiral-matrix/)|[Solution](../../blob/master/src/stevesun/algorithms/SpiralMatrix.java)|O(m*n)|O(m*n)|Medium|
 |53|[Maximum Subarray](https://leetcode.com/problems/maximum-subarray/)|[Solution](../../blob/master/src/stevesun/algorithms/MaximumSubarray.java)|O(n)|O(1)|Medium|
 |50|[Pow(x, n)](https://leetcode.com/problems/powx-n/)|[Solution](../../blob/master/src/stevesun/algorithms/PowXN.java)|O(logn)|O(logn)|Medium|
 |47|[Permutations II](https://leetcode.com/problems/permutations-ii/)|[Solution](../../blob/master/src/stevesun/algorithms/PermutationsII.java)|O(n*n!)|O(n)|Medium|Backtracking

src/stevesun/algorithms/SpiralMatrix.java

@@ -0,0 +1,69 @@
+package stevesun.algorithms;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 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].
+ */
+public class SpiralMatrix {
+
+    public List<Integer> spiralOrder(int[][] matrix) {
+        ArrayList<Integer> res = new ArrayList();
+        int row = matrix.length;
+
+        if(row == 0){
+            return res;
+        }
+        int col = matrix[0].length;
+        int len = row*col;
+
+        int i = 0, j = 0, rowStart = 1, colStart = 0;
+        while(res.size() <= len){
+            for(; j < col; j++){
+                res.add(matrix[i][j]);
+            }
+            if(res.size() == len)
+                break;
+            col--;
+            j--;
+            i++;
+            for(; i < row; i++){
+                res.add(matrix[i][j]);
+            }
+            if(res.size() == len)
+                break;
+            row--;
+            i--;
+            j--;
+            for(; j >= colStart; j--){
+                res.add(matrix[i][j]);
+            }
+            if(res.size() == len)
+                break;
+            colStart++;
+            j++;
+            i--;
+            for(; i >= rowStart; i--){
+                res.add(matrix[i][j]);
+            }
+            if(res.size() == len)
+                break;
+            rowStart++;
+            i ++;
+            j++;
+        }
+        return res;
+    }
+
+}