Create 0034 Find First and Last Position of Element in Sorted Array.md

Author: jjjllxx

binary search/0034 Find First and Last Position of Element in Sorted Array.md

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+# 34. Find First and Last Position of Element in Sorted Array
+https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array  
+Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.  
+
+If target is not found in the array, return [-1, -1].  
+
+You must write an algorithm with O(log n) runtime complexity.  
+
+
+Example 1:  
+Input: nums = [5,7,7,8,8,10], target = 8  
+Output: [3,4]  
+
+Example 2:  
+Input: nums = [5,7,7,8,8,10], target = 6  
+Output: [-1,-1]  
+
+Example 3:  
+Input: nums = [], target = 0  
+Output: [-1,-1]  
+
+Constraints:
+0 <= nums.length <= 10^5  
+-10^9 <= nums[i] <= 10^9  
+nums is a non-decreasing array.  
+-10^9 <= target <= 10^9  
+
+``` python3
+class Solution:
+    def searchRange(self, nums: List[int], target: int) -> List[int]:
+        def biSearch(nums, target):
+            left, right = 0, len(nums) - 1
+            while left <= right:
+                mid = (left + right) // 2
+                if nums[mid] >= target:
+                    right = mid - 1
+                else:
+                    left = mid + 1
+            return left
+        a = biSearch(nums, target)
+        b = biSearch(nums, target + 1)
+        if a == len(nums) or nums[a] != target:
+            return [-1, -1]
+        else:
+            return [a, b - 1]
+```