Comparison between map and hash_map in STL

1. map:

In STL of C ++, map is usedTreeSearch Algorithm; time complexity:O (log2N)

 

2. hash_map:

UseHash tableTo sort the pairs. The hash table isUse keywordsTo calculate the table location; time complexity:O (1), The worst time complexity:O (n)

In general: Hash_map is faster than map, and the search speed is basically unrelated to the data size. It belongs to the constant level, saving a certain amount of memory. If there is no need to sort it, use hash_map whenever possible.

Note:Hash returnTime consumption of hash Functions. When there are million records, map only needs 20 comparisons, and only needs 21 comparisons! So it is not necessarily a constant than log (n); use map or hash_map to weigh the following three aspects:Search speed, data volume, memory usageAnd your experience! No special standards