added misc.integer.get_local_maxima with tests

Author: jasonzhuyx

ml/misc/integer.py

@@ -3,6 +3,35 @@
 """
 
 
+def get_local_maxima(inputs: list) -> list:
+    '''
+    Find all local maxima from the input list of integers.
+
+    Examples:
+    - inputs: [11, 5, 10, 6, 4, 7, 4, 10, 1]
+      output: [11, 10, 7, 10]
+    - inputs: [1, 2, 1]
+      output; [2]
+    - inputs: [1, 2, 3, 4, 3]
+      output: [4]
+    - inputs: [1, 2, 3, 4, 4, 4, 4]
+      output: [4]
+    - inputs: [1, 4, 3, 4]
+      output: [4, 4]
+    '''
+    prev = None
+    results = []
+    siz = len(inputs)
+    for idx, v in enumerate(inputs):
+        # larger than both neighbors, or larger than left and at the end
+        larger_than_prev = prev is None or v > prev  # always True for the 1st item
+        larger_than_next = v >= inputs[idx+1] if idx+1 < siz else False
+        if larger_than_prev and (larger_than_next or idx == siz - 1):
+            results.append(v)
+        prev = v
+    return results
+
+
 def get_perfect_squares(num: int) -> list:
     """
     Get a mininum number of squares sum up to specific integer num.

tests/test_misc_integer.py

@@ -3,7 +3,9 @@
 """
 import logging
 import unittest
+import sys
 
+from ml.misc.integer import get_local_maxima
 from ml.misc.integer import get_perfect_squares
 
 
@@ -24,6 +26,64 @@ def tearDown(self):
         """tearing down at the end of the test"""
         pass
 
+    def test_get_local_maxima(self):
+        tests = [{
+            "input": [-1],
+            "output": [-1]
+        }, {
+            "input": [0],
+            "output": [0]
+        }, {
+            "input": [-sys.maxsize],
+            "output": [-sys.maxsize]
+        }, {
+            "input": [sys.maxsize],
+            "output": [sys.maxsize]
+        }, {
+            "input": [3, sys.maxsize, 0],
+            "output": [sys.maxsize]
+        }, {
+            "input": [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+            "output": [0]
+        }, {
+            "input": [7, 7, 7, 7, 7, 7, 7],
+            "output": [7]
+        }, {
+            "input": [1, 2, 1],
+            "output": [2]
+        }, {
+            "input": [-55, -2, -5],
+            "output": [-2]
+        }, {
+            "input": [-5, 2],
+            "output": [2]
+        }, {
+            "input": [5, 2],
+            "output": [5]
+        }, {
+            "input": [-1, 0, 2, 100, 10000, 123456],
+            "output": [123456]
+        }, {
+            "input": [3, 2, 1],
+            "output": [3]
+        }, {
+            "input": [1, 2, 3],
+            "output": [3]
+        }, {
+            "input": [1, 2, 1],
+            "output": [2]
+        }, {
+            "input": [1, 2, 3, 4, 3],
+            "output": [4]
+        }, {
+            "input": [1, 2, 3, 4, 4, 4, 2, 5],
+            "output": [4, 5]
+        }]
+        for test in tests:
+            expected = test["output"]
+            result = get_local_maxima(test["input"])
+            self.assertListEqual(result, expected)
+
     def test_get_perfect_squares(self):
         import random
         tests = [random.randint(1, 65535) for i in range(0, 100)]