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Add folding hashing

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Kumiho 2018-05-13 14:37:22 +02:00
parent 4ff1282433
commit 8535dc356a
1 changed files with 28 additions and 1 deletions
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29
HashTable/src/lab/HashTable.java
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@ -46,7 +46,7 @@ public class HashTable {
*/
public HashTable(int k, String hashFunction, String collisionResolution) {
this.data = new Entry[k];
this.hashFunction = hashFunction.equals("mid_square") ? 2 : 0; // TODO
this.hashFunction = hashFunction.equals("mid_square") ? 2 : hashFunction.equals("folding") ? 1 : 0;
this.probingMode = collisionResolution.equals("quadratic_probing") ? 1 : 0;
this.valueCount = 0;
this.capacity = k;
@ -277,6 +277,8 @@ public class HashTable {
private int getHashAddr(String key) {
if(this.hashFunction == 0)
return this.divisionHash(key);
else if(this.hashFunction == 1)
return this.foldingHash(key);
else if(this.hashFunction == 2)
return this.midSquareHash(key);
else
@ -299,6 +301,31 @@ public class HashTable {
return Integer.parseInt(str) % this.capacity;
}
private int foldingHash(String value) {
int addrLength = (int) Math.ceil(Math.log10(this.capacity));
String str = Long.toString(decimalRepresentation(value));
// Padd with zeroes to multiple of address length
while(str.length() % addrLength != 0) {
str = "0" + str;
}
int sum = 0;
boolean reverse = true;
String part;
for(int i = 0; i < str.length(); i += addrLength) {
part = str.substring(str.length() - (i + addrLength), str.length() - i);
if(reverse)
part = new StringBuilder(part).reverse().toString();
sum += Integer.parseInt(part);
reverse = !reverse;
}
String res = Integer.toString(sum);
return Integer.parseInt(res.substring(res.length() - addrLength, res.length())) % this.capacity;
}
private int getProbingAddr(int base, int i) {
if(this.probingMode == 0)
return (base + i) % this.capacity;