binarySearch add python3 version

算法思维系列/二分查找详解.md

@@ -508,4 +508,98 @@ int right_bound(int[] nums, int target) {
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-======其他语言代码======
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+======其他语言代码======  
+[MarineJoker](https://github.com/MarineJoker) 提供 Python3 代码  
+
+```python
+# 基本二分搜索
+def binarySearch(nums, target):
+    left = 0
+    right = len(nums) - 1
+    while left <= right:
+        mid = (left + right) // 2
+        if nums[mid] == target:
+            # 直接返回
+            return mid
+        elif nums[mid] < target:
+            left = mid + 1
+        elif nums[mid] > target:
+            right = mid - 1
+    # 直接返回
+    return -1
+
+
+# 寻找左侧边界的二分搜索，开区间写法
+def left_bound(nums, target):
+    left, right = 0, len(nums)
+    if right == 0:
+        return -1
+    while left < right:
+        mid = (left + right) // 2
+        if nums[mid] == target:
+            # 锁定边界
+            right = mid
+        elif nums[mid] < target:
+            left = mid + 1
+        elif nums[mid] > target:
+            right = mid
+    # 检查越界情况
+    if left >= len(nums) or nums[left] != target:
+        return -1
+    return left
+
+
+# 寻找右侧侧边界的二分搜索，开区间写法
+def right_bound(nums, target):
+    left, right = 0, len(nums)
+    if right == 0:
+        return -1
+    while left < right:
+        mid = (left + right) // 2
+        if nums[mid] == target:
+            # 锁定边界
+            left = mid + 1
+        elif nums[mid] < target:
+            left = mid + 1
+        elif nums[mid] > target:
+            right = mid
+    # 检查越界情况
+    if right < 0 or nums[left - 1] != target:
+        return -1
+    return left - 1
+
+
+# 左右边界闭区间写法，统一逻辑
+def left_bound(nums, target):
+    left, right = 0, len(nums) - 1
+    while left <= right:
+        mid = (left + right) // 2
+        if nums[mid] == target:
+            # 锁定边界
+            right = mid - 1
+        elif nums[mid] < target:
+            left = mid + 1
+        elif nums[mid] > target:
+            right = mid - 1
+    # 检查越界情况
+    if left >= len(nums) or nums[left] != target:
+        return -1
+    return left
+
+
+def right_bound(nums, target):
+    left, right = 0, len(nums) - 1
+    while left <= right:
+        mid = (left + right) // 2
+        if nums[mid] == target:
+            # 锁定边界
+            left = mid + 1
+        elif nums[mid] < target:
+            left = mid + 1
+        elif nums[mid] > target:
+            right = mid - 1
+    # 检查越界情况
+    if right < 0 or nums[right] != target:
+        return -1
+    return right
+```
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