Create 34_find_first_and_last_position_of_element_in_sorted_array.md

Author: Joseph Luce

leetcode/medium/34_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
+
+## Iterative binary search solution
+- Runtime: O(log(N))
+- Space: O(1)
+- N = Number of elements in array
+
+Knowing how to write a binary search whether iteratively or recursively is a must.
+However, there is a second thing being tested, whether you follow DRY (Don't repeat yourself).
+
+```
+class Solution:
+    def searchRange(self, nums: List[int], target: int) -> List[int]:
+        left_most_index = self.get_left_or_right_most_index(nums, target)
+        right_most_index = self.get_left_or_right_most_index(nums, target, search_left=False)
+        return [left_most_index, right_most_index]
+        
+    def get_left_or_right_most_index(self, nums, target, search_left=True):
+        left, right = 0, len(nums)-1
+        result_index = None
+        while left <= right:
+            mid = left + ((right - left)//2)
+            if nums[mid] == target:
+                result_index = mid
+            if search_left: # get left most index
+                if nums[mid] < target: # go right
+                    left = mid+1
+                else: # go left
+                    right = mid-1
+            else: # get right most index
+                if nums[mid] > target: # go left
+                    right = mid-1
+                else: # go right
+                    left = mid+1
+        return result_index if result_index is not None else -1
+```