HashMap

Hash map with mostly the same API as unordered_map, but ~ 3x faster. Uses 1.5x memory. Initial capacity must be a power of 2 (if provided).

8 lines

content/data-structures/HashMap.h — Simon Lindholm, chilli, source: http://codeforces.com/blog/entry/60737

#include <bits/extc++.h> 

// To use most bits rather than just the lowest ones:
struct chash { // large odd number for C
	const uint64_t C = ll(4e18 * acos(0)) | 71;
	ll operator()(ll x) const { return __builtin_bswap64(x*C); }
};
__gnu_pbds::gp_hash_table<ll,int,chash> h({},{},{},{},{1<<16});