#30 · #1429 · First Unique Number(第一个唯一数字)

Design a class that supports adding numbers to a stream and returning the first unique (non-repeating) number. Implement showFirstUnique() and add(value). If no unique number exists, return -1. Constraints: 1 <= nums.length <= 10^5, 1 <= value <= 10^8; at most 5 * 10^4 calls to add.