diff --git a/identity_matrix_recognizer.py b/identity_matrix_recognizer.py
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+++ b/identity_matrix_recognizer.py
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+# from cs 101 course of udacity.com (problem set solved solution)
+
+# Given a list of lists representing a n * n matrix as input, 
+# define a  procedure that returns True if the input is an identity matrix 
+# and False otherwise.
+
+# An IDENTITY matrix is a square matrix in which all the elements 
+# on the principal/main diagonal are 1 and all the elements outside 
+# the principal diagonal are 0. 
+# (A square matrix is a matrix in which the number of rows 
+# is equal to the number of columns)
+
+def is_identity_matrix(matrix):
+    total_elems = 0
+    last_pos = 0
+    for row in matrix:
+        total_elems += len(row)
+        if row[last_pos] == 1 and row.count(0) == len(row) - 1:
+            last_pos += 1
+        else:
+            return False
+    if total_elems == len(matrix[0]) * len(matrix[0]):
+        return True
+    else:
+        return False
+
+
+# Test Cases:
+
+matrix1 = [[1,0,0,0],
+           [0,1,0,0],
+           [0,0,1,0],
+           [0,0,0,1]]
+print is_identity_matrix(matrix1)
+#>>>True
+
+matrix2 = [[1,0,0],
+           [0,1,0],
+           [0,0,0]]
+
+print is_identity_matrix(matrix2)
+#>>>False
+
+matrix3 = [[2,0,0],
+           [0,2,0],
+           [0,0,2]]
+
+print is_identity_matrix(matrix3)
+#>>>False
+
+matrix4 = [[1,0,0,0],
+           [0,1,1,0],
+           [0,0,0,1]]
+
+print is_identity_matrix(matrix4)
+#>>>False
+
+matrix5 = [[1,0,0,0,0,0,0,0,0]]
+
+print is_identity_matrix(matrix5)
+#>>>False
+
+matrix6 = [[1,0,0,0],  
+           [0,1,0,1],  
+           [0,0,1,0],  
+           [0,0,0,1]]
+
+print is_identity_matrix(matrix6)
+#>>>False
+
+matrix7 = [[1, -1, 1],
+           [0, 1, 0],
+           [0, 0, 1]]
+print is_identity_matrix(matrix7)
+#>>>False           
+
+