add code of 54

Author: Li Li

top-interview-questions/54. Spiral Matrix.cs

@@ -0,0 +1,46 @@
+/*
+traverse right and increment rowBegin, then traverse down and decrement colEnd, 
+traverse left and decrement rowEnd, and finally I traverse up and increment colBegin.
+
+The only tricky part is that when traverse left or up, we have to check whether the 
+row or col still exists to prevent duplicates. 
+ */
+public class Solution {
+    public IList<int> SpiralOrder(int[,] matrix) {
+        List<int> res = new List<int>();
+        if (matrix.GetLength(0) == 0) {
+            return res;
+        }
+        int rowBegin = 0;
+        int rowEnd = matrix.GetLength(0) - 1;
+        int colBegin = 0;
+        int colEnd = matrix.GetLength(1) - 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--;
+            if (rowBegin <= rowEnd) {
+                // traverse left
+                for (int i = colEnd; i >= colBegin; i--) {
+                    res.Add(matrix[rowEnd, i]);
+                }
+            }
+            rowEnd--;
+            if (colBegin <= colEnd) {
+                // traverse up
+                for (int i = rowEnd; i >= rowBegin; i--) {
+                    res.Add(matrix[i, colBegin]);
+                }
+            }
+            colBegin++;
+        }
+        return res;
+    }
+}