Merge pull request #108 from jerryderry/bsearch-variant-python

Binary search variants in python

python/16_bsearch/bsearch_variants.py

@@ -0,0 +1,77 @@
+"""
+    Author: Wenru
+"""
+
+from typing import List
+
+def bsearch_left(nums: List[int], target: int) -> int:
+    """Binary search of the index of the first element
+    equal to a given target in the ascending sorted array.
+    If not found, return -1.
+    """
+    low, high = 0, len(nums) - 1
+    while low <= high:
+        mid = low + (high - low) // 2
+        if nums[mid] < target:
+            low = mid + 1
+        else:
+            high = mid - 1
+    return low if nums[low] == target else -1
+
+def bsearch_right(nums: List[int], target: int) -> int:
+    """Binary search of the index of the last element
+    equal to a given target in the ascending sorted array.
+    If not found, return -1.
+    """
+    low, high = 0, len(nums) - 1
+    while low <= high:
+        mid = low + (high - low) // 2
+        if nums[mid] <= target:
+            low = mid + 1
+        else:
+            high = mid - 1
+    return high if nums[high] == target else -1
+
+
+def bsearch_left_not_less(nums: List[int], target: int) -> int:
+    """Binary search of the index of the first element
+    not less than a given target in the ascending sorted array.
+    If not found, return -1.
+    """
+    low, high = 0, len(nums) - 1
+    while low <= high:
+        mid = low + (high - low) // 2
+        if nums[mid] < target:
+            low = mid + 1
+        else:
+            high = mid - 1
+    return low if low < len(nums) else -1
+
+def bsearch_right_not_greater(nums: List[int], target: int) -> int:
+    """Binary search of the index of the last element
+    not greater than a given target in the ascending sorted array.
+    If not found, return -1.
+    """
+    low, high = 0, len(nums) - 1
+    while low <= high:
+        mid = low + (high - low) // 2
+        if nums[mid] <= target:
+            low = mid + 1
+        else:
+            high = mid - 1
+    return high if high > 0 else -1
+
+if __name__ == "__main__":
+    import bisect
+
+    a = [0, 1, 1, 2, 3, 4, 5, 6, 6, 7, 8, 8, 10, 10, 10]
+    b = [11, 12, 12, 13, 14, 14, 15, 15]
+    print(bisect.bisect_left(a, 10) == bsearch_left(a, 10))
+    print(bisect.bisect_right(a, 10))
+    print(bisect.bisect_right(a, 6)-1 == bsearch_right(a, 6))
+    print(bisect.bisect_right(b, 14)-1 == bsearch_right(b, 14))
+
+    print(bsearch_left_not_less(a, 11))
+    print(bsearch_right_not_greater(b, 12))
+    print(bsearch_right_not_greater(b, 10))
+    print(bsearch_right_not_greater(b, 17))