add python code

public/py/ch2/halfsearch/binary_search.py

@@ -0,0 +1,43 @@
+"""
+二分查找 — 在有序数组中查找目标值
+时间复杂度 O(log n)
+"""
+
+def binary_search_recursive(arr, target, left, right):
+    """递归版二分查找"""
+    if left > right:
+        return -1
+
+    mid = left + (right - left) // 2
+
+    if arr[mid] == target:
+        return mid
+    elif arr[mid] > target:
+        return binary_search_recursive(arr, target, left, mid - 1)
+    else:
+        return binary_search_recursive(arr, target, mid + 1, right)
+
+def binary_search_iterative(arr, target):
+    """迭代版二分查找"""
+    left, right = 0, len(arr) - 1
+
+    while left <= right:
+        mid = left + (right - left) // 2
+        if arr[mid] == target:
+            return mid
+        elif arr[mid] > target:
+            right = mid - 1
+        else:
+            left = mid + 1
+
+    return -1
+
+if __name__ == "__main__":
+    arr = [1, 3, 5, 7, 9, 11, 13, 15]
+    target = 7
+
+    idx1 = binary_search_recursive(arr, target, 0, len(arr) - 1)
+    idx2 = binary_search_iterative(arr, target)
+
+    print(f"数组: {arr}")
+    print(f"查找 {target}: 递归版结果索引={idx1}, 迭代版结果索引={idx2}")