Value equal to index value

Author: anantkaushik

Apple/Problem#273.py

@@ -0,0 +1,16 @@
+"""
+A fixed point in an array is an element whose value is equal to its index. 
+Given a sorted array of distinct elements, return a fixed point, if one exists. Otherwise, return False.
+For example, given [-6, 0, 2, 40], you should return 2. Given [1, 5, 7, 8], you should return False.
+"""
+def fixed_point(arr):
+    start, end = 0, len(arr)-1
+    while start <= end:
+        mid = (start+end)//2
+        if arr[mid] == mid:
+            return mid
+        elif arr[mid] < mid:
+            start = mid + 1
+        else:
+            end = mid - 1
+    return False