private String makeRange(int a, int b) {
        if (a == b) {
            return String.valueOf(a);
        } else {
            return a + "->" + b;
        }
    }
Given a sorted integer array where the range of elements are in the inclusive range [lower, upper], return its missing ranges.
For example, given [0, 1, 3, 50, 75], lower = 0 and upper = 99, return ["2", "4->49", "51->74", "76->99"].

Time complexity O(n)

https://leetcode.com/problems/missing-ranges/
src/com/interview/array/MissingRanges.java