solves matrix diagonal sum

Author: anishLearnsToCode

README.md

@@ -393,3 +393,4 @@
 | 1556 | [Thousand Separator](https://leetcode.com/problems/thousand-separator)                                                                               |                                                                [![Java](assets/java.png)](src/ThousandSeparator.java)                                                                |                                                                                                                                   |
 | 1560 | [Most Visited Sector in a Circular Track](https://leetcode.com/problems/most-visited-sector-in-a-circular-track)                                     |                                                        [![Java](assets/java.png)](src/MostVisitedSectorInACircularTrack.java)                                                        |                                                                                                                                   |
 | 1566 | [Detect Pattern of Length M Repeated K or More Times](https://leetcode.com/problems/detect-pattern-of-length-m-repeated-k-or-more-times)             |                                                   [![Java](assets/java.png)](src/DetectPatternOfLengthMRepeatedKOrMoreTimes.java)                                                    |                                                                                                                                   |
+| 1572 | [Matrix Diagonal Sum](https://leetcode.com/problems/matrix-diagonal-sum)                                                                             |                                                                [![Java](assets/java.png)](src/MatrixDiagonalSum.java)                                                                |                                                                                                                                   |

src/MatrixDiagonalSum.java

@@ -0,0 +1,26 @@
+// https://leetcode.com/problems/matrix-diagonal-sum
+// T: O(N)
+// S: O(1)
+
+public class MatrixDiagonalSum {
+    public int diagonalSum(int[][] matrix) {
+        return sumPrimaryDiagonal(matrix) + sumSecondaryDiagonal(matrix) -
+                ((matrix.length & 1) == 1 ? matrix[matrix.length / 2][matrix.length / 2] : 0);
+    }
+
+    private int sumPrimaryDiagonal(int[][] matrix) {
+        int sum = 0;
+        for (int i = 0 ; i < matrix.length ; i++) {
+            sum += matrix[i][i];
+        }
+        return sum;
+    }
+
+    private int sumSecondaryDiagonal(int[][] matrix) {
+        int sum = 0;
+        for (int i = 0 ; i < matrix.length ; i++) {
+            sum += matrix[i][matrix.length - 1 - i];
+        }
+        return sum;
+    }
+}