41 lines
1.3 KiB
C++
41 lines
1.3 KiB
C++
#include <unordered_map>
|
||
#include <iostream>
|
||
#include <string>
|
||
using namespace std;
|
||
|
||
class hashdef{
|
||
public:
|
||
//template<class T>，不太好分类型，就直接用string了
|
||
size_t operator()(const string& a) const{//这里必须有const，在hash内部会把其当const调用
|
||
//同样不能有static，调用需要用到this
|
||
int hash;
|
||
int seed = 114514;
|
||
for(char x : a){
|
||
hash += static_cast<int>(x)*31 + seed;
|
||
hash %= 1009;
|
||
}
|
||
return hash;
|
||
}
|
||
};
|
||
int main(){
|
||
hashdef a;
|
||
unordered_map<string, string, hashdef> m1{make_pair("1","111")};
|
||
unordered_map<string, string> m2;
|
||
m1.insert({make_pair("2","222"),make_pair("3","333"),make_pair("6","666"),make_pair("5","555")});
|
||
//下面首先查看哈希值
|
||
cout << a("1") << " " << a("2") << " " << a("3") << " " << a("5") << " " << a("6") << endl;
|
||
m1.rehash(1000);//重新设置桶的个数为1009，配合hash(此时会重新计算所有hash)
|
||
m2.max_load_factor(0.7f);//重新设置-控制扩容-负载因子=元素个数/桶个数，这里是平均每个桶最多0.7个元素
|
||
cout << "bucket_count: " << m1.bucket_count() << endl;//hashtable_policy.h中的质数表跳转到最近的大于n的数
|
||
cout << m1.max_load_factor() << " " << m1.load_factor() << endl;
|
||
m1["7"] = "777";
|
||
cout << m1.at("6") << " " << m1["5"] << " " << m1.find("6")->second << endl;
|
||
return 0;
|
||
}
|
||
/*
|
||
1007 29 60 122 153
|
||
bucket_count: 1031
|
||
1 0.00484966
|
||
666 555 666
|
||
*/
|