给定一个字符串,找到它的第一个不重复的字符,并返回它的索引。如果不存在,则返回 -1。
案例:
s = "leetcode"
返回 0.
s = "loveleetcode",
返回 2.
public class solu {
public int ff(String s){
int[] li=new int[26];
for (int i=0;i<s.length();i++)
li[s.charAt(i)-'a'] ++;
for (int i =0;i<s.length();i++)
if(li[s.charAt(i)-'a']==1)
return i;
return -1;
}
public static void main(String[] args) {
solu so=new solu();
System.out.println(so.ff("vavavadfs"));
}
}
C++
class Solution {
public:
int firstUniqChar(string s) {
int n=s.size();
map<char,int> mp;
for(int i=0;i<n;i++)
mp[s[i]]+=1;
for(int i=0;i<n;i++)
if(mp[s[i]]==1)
return i;
return -1;
}
};
其中 int[26] li 就是一个哈希表
哈希函数的设计
小范围正整数直接使用
小范围负整数可以偏移成正整数
import java.util.Map;
import java.util.TreeMap;
public class HashTable<K, V> {
private static final int upperTol = 10;
private static final int lowerTol = 2;
private static final int initCapacity = 7;
private TreeMap<K, V>[] hashtable;
private int size;
private int M;
public HashTable(int M){
this.M = M;
size = 0;
hashtable = new TreeMap[M];
for(int i = 0 ; i < M ; i ++)
hashtable[i] = new TreeMap<>();
}
public HashTable(){
this(initCapacity);
}
private int hash(K key){
return (key.hashCode() & 0x7fffffff) % M;
}
public int getSize(){
return size;
}
public void add(K key, V value){
TreeMap<K, V> map = hashtable[hash(key)];
if(map.containsKey(key))
map.put(key, value);
else{
map.put(key, value);
size ++;
if(size >= upperTol * M)
resize(2 * M);
}
}
public V remove(K key){
V ret = null;
TreeMap<K, V> map = hashtable[hash(key)];
if(map.containsKey(key)){
ret = map.remove(key);
size --;
if(size <= lowerTol * M && M > initCapacity)
resize(M / 2);
}
return ret;
}
public void set(K key, V value){
TreeMap<K, V> map = hashtable[hash(key)];
if(!map.containsKey(key))
throw new IllegalArgumentException(key + " doesn't exist!");
map.put(key, value);
}
public boolean contains(K key){
return hashtable[hash(key)].containsKey(key);
}
public V get(K key){
return hashtable[hash(key)].get(key);
}
private void resize(int newM){
TreeMap<K, V>[] newHashTable = new TreeMap[newM];
for(int i = 0 ; i < newM ; i ++)
newHashTable[i] = new TreeMap<>();
for(int i = 0 ; i < M ; i ++)
for(K key: hashtable[i].keySet())
newHashTable[hash(key)].put(key, hashtable[i].get(key));
this.M = newM;
this.hashtable = newHashTable;
}
}