Unbounded Binary Search

Given a monotonically increasing function f(x), find the value of x where f(x) becomes positive for the first time. In other words, find a positive integer x such that f(x-1), f(x-2),… are negative and f(x+1), f(x+2),… are positive.

Find the odd occurring element in log(n) time

Given an array of integers where every element appears even number of times except one element which appears odd number of times, find that odd occurring element in O(log(n)) time and constant space.