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move const to before type

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Jidong Xiao
2025-03-31 19:45:16 -04:00
committed by JamesFlare
parent 51d388be7c
commit b33e6b0376
1 changed files with 7 additions and 3 deletions
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10
lectures/22_hash_tables_I/README.md
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@@ -158,7 +158,7 @@ despite the actual distribution of keys that are to be stored.
satisfy the second. satisfy the second.
- Another example of a dangerous hash function on string keys is to add or multiply the ascii values of each char: - Another example of a dangerous hash function on string keys is to add or multiply the ascii values of each char:
```cpp ```cpp
unsigned int hash(string const& k, unsigned int N) { unsigned int hash(const std::string& k, unsigned int N) {
unsigned int value = 0; unsigned int value = 0;
for (unsigned int i=0; i<k.size(); ++i) { for (unsigned int i=0; i<k.size(); ++i) {
value += k[i]; // conversion to int is automatic value += k[i]; // conversion to int is automatic
@@ -166,12 +166,16 @@ unsigned int hash(string const& k, unsigned int N) {
return value % N; return value % N;
} }
``` ```
The problem is that different permutations of the same string result in the same hash table location. The problem is its high collision rate:
1. Anagrams (e.g., "listen" and "silent") get the same hash.
2. Many different strings can sum to the same value, leading to collisions.
- This can be improved through multiplications that involve the position and value of the key: - This can be improved through multiplications that involve the position and value of the key:
```cpp ```cpp
unsigned int hash(string const& k, unsigned int N) { unsigned int hash(const std::string& k, unsigned int N) {
unsigned int value = 0; unsigned int value = 0;
for (unsigned int i=0; i<k.size(); ++i) { for (unsigned int i=0; i<k.size(); ++i) {
value = value*8 + k[i]; // conversion to int is automatic value = value*8 + k[i]; // conversion to int is automatic