GfG: Missing in a Sorted Array of Natural Numbers

Problem12.py

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+# Given a sorted array arr[] of n-1 integers, these integers are in the range of 1 to n. There are no duplicates in the array. One of the integers is missing in the array. Find the missing integer. 
+# Examples: 
+
+# Input : arr[] = [1, 2, 3, 5, 6, 7, 8]
+# Output : 5
+# Explanation: The missing integer in the above array is 5 
+
+# Input : arr[] = [1, 2, 3, 4, 5, 6, 8, 9]
+# Output : 7
+# Explanation: The missing integer in the above array is 7 
+
+
+# Time Complexity : O(log n)
+# Space Complexity :O(1)
+# Did this code successfully run on Leetcode : ran of GfG
+# Any problem you faced while coding this : no
+
+#Approach: after every iteration, low only ever advances into the true condition and wont proceed the false condition so it becomes easy to track low
+
+
+def findMissingInteger(arr):
+    n=len(arr)+1 #plus 1 for actual length since current arr has 1 less
+    if n==1: return 1
+    low=0
+    high=len(arr)-1
+
+    while(low<=high):
+        mid=(low+high)//2
+        if(arr[mid]==mid+1):
+            low=mid+1
+        else:
+            high=mid-1
+    return low+1