python saddle points

python/saddle-points/.exercism/metadata.json

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+{"track":"python","exercise":"saddle-points","id":"142ada3a5e35437baa24b9bddb78a991","url":"https://exercism.io/my/solutions/142ada3a5e35437baa24b9bddb78a991","handle":"Xevion","is_requester":true,"auto_approve":false}

python/saddle-points/README.md

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+# Saddle Points
+
+Detect saddle points in a matrix.
+
+So say you have a matrix like so:
+
+```text
+    1  2  3
+  |---------
+1 | 9  8  7
+2 | 5  3  2     <--- saddle point at (2,1)
+3 | 6  6  7
+```
+
+It has a saddle point at (2, 1).
+
+It's called a "saddle point" because it is greater than or equal to
+every element in its row and less than or equal to every element in
+its column.
+
+A matrix may have zero or more saddle points.
+
+Your code should be able to provide the (possibly empty) list of all the
+saddle points for any given matrix.
+
+Note that you may find other definitions of matrix saddle points online,
+but the tests for this exercise follow the above unambiguous definition.
+
+## Exception messages
+
+Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to
+indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not
+every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include
+a message.
+
+To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
+`raise Exception`, you should write:
+
+```python
+raise Exception("Meaningful message indicating the source of the error")
+```
+
+## Running the tests
+
+To run the tests, run the appropriate command below ([why they are different](https://github.com/pytest-dev/pytest/issues/1629#issue-161422224)):
+
+- Python 2.7: `py.test saddle_points_test.py`
+- Python 3.4+: `pytest saddle_points_test.py`
+
+Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
+`python -m pytest saddle_points_test.py`
+
+### Common `pytest` options
+
+- `-v` : enable verbose output
+- `-x` : stop running tests on first failure
+- `--ff` : run failures from previous test before running other test cases
+
+For other options, see `python -m pytest -h`
+
+## Submitting Exercises
+
+Note that, when trying to submit an exercise, make sure the solution is in the `$EXERCISM_WORKSPACE/python/saddle-points` directory.
+
+You can find your Exercism workspace by running `exercism debug` and looking for the line that starts with `Workspace`.
+
+For more detailed information about running tests, code style and linting,
+please see [Running the Tests](http://exercism.io/tracks/python/tests).
+
+## Source
+
+J Dalbey's Programming Practice problems [http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html](http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html)
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

python/saddle-points/saddle_points.py

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+def saddle_points(matrix):
+    # Check a single point in the matrix for if it's a saddle point
+    def saddle(point):
+        row = matrix[point[0]]
+        column = [row[point[1]] for row in matrix]
+        return max(row) == row[point[1]] and min(column) == column[point[0]]
+    # Raise a value error if the matrix lengths are not consistent
+    if len(set(list(map(len, matrix)))) > 1:
+        d = {i : len(m) for i, m in enumerate(matrix)}
+        d = sorted(list(set(list(d.values()))), reverse=True)
+        raise ValueError(f'Matrix Length of {d[-1]} instead of usual {d[0]} found.')
+    saddles = []
+    # Check every point for if it's a saddle point
+    for x, row in enumerate(matrix):
+        for y, point in enumerate(row):
+            if saddle((x, y)):
+                saddles.append({'row' : x + 1, 'column' : y + 1})
+    return saddles or [{}]

python/saddle-points/saddle_points_test.py

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+"""Tests for the saddle-points exercise
+
+Implementation note:
+The saddle_points function must validate the input matrix and raise a
+ValueError with a meaningful error message if the matrix turns out to be
+irregular.
+"""
+import unittest
+
+from saddle_points import saddle_points
+
+
+# Tests adapted from `problem-specifications//canonical-data.json` @ v1.5.0
+
+class SaddlePointsTest(unittest.TestCase):
+    def test_identify_single_saddle_point(self):
+        matrix = [[9, 8, 7], [5, 3, 2], [6, 6, 7]]
+        self.assertEqual(saddle_points(matrix), [{"row": 2, "column": 1}])
+
+    def test_empty_matrix_has_no_saddle_points(self):
+        self.assertEqual(saddle_points([]), [dict()])
+
+    def test_matrix_with_one_elem_has_single_saddle_point(self):
+        matrix = [[1]]
+        self.assertEqual(saddle_points(matrix), [{"row": 1, "column": 1}])
+
+    def test_identify_lack_of_saddle_points_when_there_are_none(self):
+        matrix = [[1, 2, 3], [3, 1, 2], [2, 3, 1]]
+        self.assertEqual(saddle_points(matrix), [dict()])
+
+    def test_identify_multiple_saddle_points_in_column(self):
+        matrix = [[4, 5, 4], [3, 5, 5], [1, 5, 4]]
+        expected = [{"row": 1, "column": 2}, {"row": 2, "column": 2},
+                    {"row": 3, "column": 2}]
+        self.assertEqual(saddle_points(matrix), expected)
+
+    def test_identify_multiple_saddle_points_in_row(self):
+        matrix = [[6, 7, 8], [5, 5, 5], [7, 5, 6]]
+        expected = [{"row": 2, "column": 1}, {"row": 2, "column": 2},
+                    {"row": 2, "column": 3}]
+        self.assertEqual(saddle_points(matrix), expected)
+
+    def test_identify_saddle_point_in_bottom_right_corner(self):
+        matrix = [[8, 7, 9], [6, 7, 6], [3, 2, 5]]
+        expected = [{"row": 3, "column": 3}]
+        self.assertEqual(saddle_points(matrix), expected)
+
+    def test_non_square_matrix_with_2_saddle_points(self):
+        matrix = [[3, 1, 3], [3, 2, 4]]
+        self.assertEqual(saddle_points(matrix), [{"row": 1, "column": 1},
+                                                 {"row": 1, "column": 3}])
+
+    def test_single_column_matrix_has_saddle_point_min_value(self):
+        matrix = [[2], [1], [4], [1]]
+        self.assertEqual(saddle_points(matrix), [{"row": 2, "column": 1},
+                                                 {"row": 4, "column": 1}])
+
+    def test_single_row_matrix_has_saddle_point_in_max_value(self):
+        matrix = [[2, 5, 3, 5]]
+        self.assertEqual(saddle_points(matrix), [{"row": 1, "column": 2},
+                                                 {"row": 1, "column": 4}])
+
+    # Additional tests for this track
+
+    def test_irregular_matrix(self):
+        matrix = [[3, 2, 1], [0, 1], [2, 1, 0]]
+        with self.assertRaisesWithMessage(ValueError):
+            saddle_points(matrix)
+
+    # Utility functions
+    def setUp(self):
+        try:
+            self.assertRaisesRegex
+        except AttributeError:
+            self.assertRaisesRegex = self.assertRaisesRegexp
+
+    def assertRaisesWithMessage(self, exception):
+        return self.assertRaisesRegex(exception, r".+")
+
+
+if __name__ == '__main__':
+    unittest.main()