In an array or list Z [] containing integers, an identity index is an index where A[i] = i, i.e. the value of the element at that index equals the index itself. Write a method to return an identity index from a sorted list of distinct integers, if such an index exists, or -1 if it doesn't. Use time complexity O(logN) only. Use Python to solve this.

Example:

identityIndex([-5, -20, 0, 3, 4]) == 3, because Z[3] == 3 identityIndex([7, 4, 5, 7, 9]) == -1, because Z[2] == i isn't true for any i