今天在复习Arrays and String 时看到一个很有趣的问题。希望跟大家分享一下。

Implement the hash table using array / binary search tree

1.  Using Array/LinkedList:

1) key需要通过hash 来得到array中的index

2) array的每一位都是放着一个list

3) 需要自己定义一个class,list 由这个class 类型组成

4) 要考虑到万一hashvalue 范围很大,需要把table的size压缩: %TABLE_SIZE;

class LinkedHashEntry {
String key;
int value;
LinkedHashEntry next;
LinkedHashEntry(String key, int value) {
this.key = key;
this.value = value;
this.next = null;
} } public class HashTable { private int TABLE_SIZE;
private int size;
private LinkedHashEntry[] table; // Constructor
HashTable(int ts) {
size = 0;
TABLE_SIZE = ts;
table = new LinkedHashEntry[TABLE_SIZE];
for(int i = 0; i < TABLE_SIZE; i ++) {
table[i] = null;
}
} // hash function
private int myhash(String key) {
int hashValue = key.hashCode();
hashValue %= TABLE_SIZE;
if(hashValue < 0) {
hashValue += TABLE_SIZE;
}
return hashValue;
}
// hash put function public void put(String key, int value) {
int hash = (myhash(key) % TABLE_SIZE);
if(table[hash] == null) {
table[hash] = new LinkedHashEntry(key, value);
} else {
LinkedHashEntry entry = table[hash];
while(entry.next != null && !entry.key.equals(key)) {
entry = entry.next;
}
if(entry.key.equals(key)) {
entry.value = value; // if we have already put this pair of key value
} else {
entry.next = new LinkedHashEntry(key, value);
}
}
size ++;
} public int getValue(String key) {
int hash = (myhash(key) % TABLE_SIZE);
if(table[hash] == null) {
return -1;
} else {
LinkedHashEntry entry = table[hash];
while(entry.next != null && !entry.key.equals(key)) { entry = entry.next;
}
if(entry.key.equals(key)) {
return entry.value;
} else {
return -1;
}
}
} public void remove(String key, int value) {
int hash = (myhash(key)% TABLE_SIZE);
if(table[hash] == null) {
return;
} else {
LinkedHashEntry preEntry = null;
LinkedHashEntry entry = table[hash];
while(entry.next != null && !entry.key.equals(key)) {
preEntry = entry;
entry = entry.next;
}
if(entry.key.equals(key)) {
if(preEntry == null) {
table[hash] = entry.next;
} else {
preEntry.next = entry.next;
}
size --;
}
}
} public int size() {
return size;
} }

  

2. Using BST

在craking coding interview 这本书上看到这个问题,但是并没有想清楚这个问题的解决方法,希望有大神可以解答。谢谢!

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