UVa 11572: Unique Snowflakes problem description: Given a list of snowflakes (integers), print the length of the longest sublist in which all of the snowflakes are unique. This problem can be solved using an STL map. A map is a container that maps keys of any type to values of any type and does lookups, insertions, and deletions in O(log n), where n is the number of elements in the map. Internally, STL maps are usually implemented as red-black trees. In short, the map is a good STL container to become acquainted with! For this problem, we use a map to keep track of the index of the last occurance of each snowflake. Normally one could also use a vector or array for this purpose, but in this case there are too many possible snowflakes(10^9). But since we are guaranteed that there will be no more than one million snowflakes total, we can get away with using a map, because the map, unlike the vector, only stores the keys it needs to. Thus our map will be of size one million tops, whereas a vector or array implementation would consistently be of size 10^9, which is too big to fit into memory. This algorithm also uses variables cnt and block. cnt stores the number of unique snowflakes seen so far, and block stores the index of the last snowflake that wasn’t unique. When the algorithm finds a snowflake that isn’t unique, it resets cnt to the number of snowflakes between the most recent “conflict” (a snowflake that was found to not be unique) and the current index, and updates block to reflect the new most recent collision. Every iteration, the variable ans is calculated as the max of itself and the current value of cnt, which ensures that the algorithm always finds the largest range.