update binary search

Author: KaidiGuo

Binary Search/34. Find First and Last Position of Element in Sorted Array.py

@@ -0,0 +1,26 @@
+# very similar to the basic binary search
+# the only difference is the target value can repeat n times in the list, so once you locate the mid that eaqual to the target number
+# you need two pointers from the mid to find the left and right boundary index that gives you the same value as the target
+
+class Solution:
+    def searchRange(self, nums: List[int], target: int) -> List[int]:
+        l = 0
+        r = len(nums)-1
+        while l <= r:
+            mid = l +(r-l)//2
+            if nums[mid] == target:
+                l = mid
+                r = mid
+                
+                while l >=0 and nums[l] == target :
+                    l -= 1                   
+                   
+                while r <=len(nums)-1 and nums[r] == target :
+                    r +=1
+            
+                return [l+1,r-1]
+            elif nums[mid] > target:
+                r = mid -1
+            elif nums[mid] < target:
+                l = mid + 1
+        return [-1,-1]