向量< double& gt;的哈希函数 [英] Hash function for vector<double>

问题描述

首先，我想知道是否有人知道代表n维向量的向量的哈希函数吗?

First, I am wondering if anyone knows of a hash function for vector representing an n-D vector?

第二，是否有类似的哈希函数，我可以在其中指定分辨率，以使两个闭合"向量哈希为相同值?

Second, is there a similar hash function where I can specify a resolution such that two "close" vectors hash to the same value?

例如: 给定分辨率r = 0.01 q1 = {1.01，2.3} q2 = {1.01，2.31} 会散列为相同的值.

For example: given resolution r = 0.01 q1 = {1.01, 2.3} q2 = {1.01, 2.31} would hash to the same value.

感谢您的帮助！

推荐答案

也许这样的方法对您有用?

Perhaps something like this would work for you?

#include <stdint.h>
#include <iostream>
#include <vector>

using namespace std;

// simple variant of ELF hash ... but you could use any general-purpose hashing algorithm here instead
static int GetHashCodeForBytes(const char * bytes, int numBytes)
{
   unsigned long h = 0, g;
   for (int i=0; i<numBytes; i++)
   {
      h = ( h << 4 ) + bytes[i];
      if (g = h & 0xF0000000L) {h ^= g >> 24;}
      h &= ~g;
   }
   return h;
}

static int GetHashForDouble(double v)
{
   return GetHashCodeForBytes((const char *)&v, sizeof(v));
}

static int GetHashForDoubleVector(const vector<double> & v)
{
   int ret = 0;
   for (int i=0; i<v.size(); i++) ret += ((i+1)*(GetHashForDouble(v[i])));
   return ret;
}

int main()
{
   vector<double> vec;
   vec.push_back(3.14159);
   vec.push_back(2.34567);
   cout << "  Hash code for test vec is:  " << GetHashForDoubleVector(vec) << endl;
   return 0;
}

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