unique character in string
Implement an algorithm to determine if a string has all unique characters.
you can not use additional data structures?
请大侠指点
谢谢

[解决办法]
Use hash table to detect if there is repeated characters,When hash collision occurs,there must be characteres that is not unique.
The time complicity and space complexity are both O(n).
[解决办法]
如果允许破坏原来的数据，那么可以排序，在排序中判断是否有相等的，相等则跳出。

由于排序可以达到O(nlogn),所以这个方法不会低于O(nlogn)。