Create 1572-matrix-diagonal-sum.js

Author: everthis

1572-matrix-diagonal-sum.js

@@ -0,0 +1,16 @@
+/**
+ * @param {number[][]} mat
+ * @return {number}
+ */
+const diagonalSum = function(mat) {
+  let res = 0, n = mat.length
+  for(let i = 0; i < n; i++) {
+    const j = i, ii = i, jj = n - 1 - i
+    if(j == jj) res += mat[i][j]
+    else {
+      res += mat[i][j] + mat[ii][jj]
+    }
+  }
+  
+  return res
+};