C++ 使用Rabin-Karp进行模式搜索
我正在使用递推公式研究Rabin-Karp算法。下面是代码。 在代码中,我检查以正常方式和递归公式计算的哈希值。两个值不匹配。我花了足够的时间调试了将近3个小时,不确定是什么问题。请求您帮助查找错误C++ 使用Rabin-Karp进行模式搜索,c++,string,algorithm,stl,rabin-karp,C++,String,Algorithm,Stl,Rabin Karp,我正在使用递推公式研究Rabin-Karp算法。下面是代码。 在代码中,我检查以正常方式和递归公式计算的哈希值。两个值不匹配。我花了足够的时间调试了将近3个小时,不确定是什么问题。请求您帮助查找错误 #include <iostream> #include <fstream> #include <streambuf> #include <cstdint> #include <string> #include <vector>
#include <iostream>
#include <fstream>
#include <streambuf>
#include <cstdint>
#include <string>
#include <vector>
const std::uint64_t uiLargePrime = 1000000007;
const unsigned int uiXValue = 263;
const unsigned int uiHashTableSize = 79;
struct sCalcHash {
std::uint64_t operator() (const std::string& strText) {
// user horners method.
unsigned int uiStrLength = strText.length();
std::uint64_t uiResult = 0;
// calculate hash value
for(int uiIdx = (uiStrLength - 1); uiIdx >= 0; uiIdx--) {
uiResult = (((uiResult * uiXValue) % uiLargePrime) + strText[uiIdx]) % uiLargePrime ;
}
// return uiResult % uiHashTableSize;
return uiResult;
}
};
// calculate x ^ uiPatternLength % uiLargePrime.
unsigned int expValueOfX(unsigned int uiXVal, unsigned int uiPower) {
// get X value in range of prime;
uiXVal = uiXVal % uiLargePrime;
unsigned int uiResult = 1;
while (uiPower > 0 ) {
// check if power is odd
if (uiPower & 1) {
uiResult = ((uiResult % uiLargePrime) * (uiXVal % uiLargePrime) ) % uiLargePrime;
}
// now uiPower is even
uiPower = uiPower >> 1;
uiXVal = ((uiXVal % uiLargePrime) * (uiXVal % uiLargePrime)) % uiLargePrime;
}
return uiResult;
}
// Rabin Karp Algorithm
void RabinKarpAlgo(std::string& Text, std::string& pattern) {
std::vector<unsigned int> vecPostions;
//calculate hash value of pattern.
sCalcHash hash;
std::uint64_t hashValPattern = hash(pattern);
std::cout << "Hash Value of pattern: " << hashValPattern << std::endl;
unsigned int uiPatternLength = pattern.length();
// calculate x ^ uiPatternLength % uiLargePrime.
unsigned int uiXExpVal = expValueOfX(uiXValue, uiPatternLength);
//std::cout << "Exponential value " << uiXExpVal << std::endl;
// calculate hash value
unsigned int uiStrLength = Text.length();
// calculate hash value of last part of string of pattern length.
unsigned int uiLastIdx = uiStrLength - uiPatternLength;
std::uint64_t hashValLastIdx = hash(Text.substr(uiLastIdx));
std::cout << "Hash Value of last indx of text: " << hashValLastIdx << std::endl;
// if hash value is same then compare string
if (hashValLastIdx == hashValPattern) {
if(pattern == Text.substr(uiLastIdx)) {
std::cout << "Pushing index: " << uiLastIdx << std::endl;
vecPostions.push_back(uiLastIdx);
}
}
for(int uiIdx = uiLastIdx - 1; uiIdx >= 0; uiIdx--) {
// calculate hash value of string
std::int64_t iHashValRecur = ( (Text[uiIdx] % uiLargePrime) +
((hashValLastIdx % uiLargePrime) * (uiXValue % uiLargePrime)) % uiLargePrime -
((Text[uiIdx + uiPatternLength] % uiLargePrime) * (uiXExpVal % uiLargePrime) ) % uiLargePrime
) % uiLargePrime;
unsigned int iHashVal = hash(Text.substr(uiIdx, uiPatternLength));
std::cout << "Hash Value of with recurr " << uiIdx << " is " << iHashValRecur << " and with hash func: " << iHashVal << std::endl;
if(iHashValRecur == hashValPattern) {
// compare string
if(pattern == Text.substr(uiIdx, uiPatternLength) ) {
std::cout << "Pushing index: " << uiIdx << std::endl;
vecPostions.push_back(uiIdx);
}
}
hashValLastIdx = iHashValRecur;
}
// print vectors
for( int uiIdx = vecPostions.size() - 1; uiIdx >= 0; uiIdx--) {
std::cout << vecPostions[uiIdx] << " ";
}
std::cout << std::endl;
return ;
}
int main() {
std::ifstream inputFile("rabinkarp.in");
std::streambuf *pCinbuf = std::cin.rdbuf();
std::cin.set_rdbuf(inputFile.rdbuf());
std::string strText;
std::string strPattern;
std::cin >> strPattern;
std::cin >> strText;
std::cout << "Text: " << strText << std::endl;
std::cout << "Pattern: " << strPattern << std::endl;
RabinKarpAlgo(strText, strPattern);
return 0;
}
Text: baaaaaaa
Pattern: aaaaa
Hash Value of pattern: 853306522
Hash Value of last indx of text: 853306522
Pushing index: 3
Hash Value of with recurr 2 is 435650523 and with hash func: 853306522
Hash Value of with recurr 1 is 9779548 and with hash func: 853306522
Hash Value of with recurr 0 is 5713908 and with hash func: 853306523
3
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常数std::uint64\u t uiLargePrime=100000007;
常量无符号整数uiXValue=263;
常量unsigned int uiHashTableSize=79;
结构尺度{
std::uint64_t运算符()(常量std::string和strText){
//用户霍纳斯方法。
unsigned int uiStrLength=strText.length();
标准::uint64_t uiResult=0;
//计算散列值
对于(int-uiIdx=(uiStrLength-1);uiIdx>=0;uiIdx--){
uiResult=((uiResult*uiXValue)%uiLargePrime)+strText[uiIdx])%uiLargePrime;
}
//返回uiResult%uiHashTableSize;
返回结果;
}
};
//计算x^uiPatternLength%uiLargePrime。
unsigned int expValueOfX(unsigned int uiXVal,unsigned int uiPower){
//得到素数范围内的X值;
uiXVal=uiXVal%uiLargePrime;
无符号整数uiResult=1;
而(uiPower>0){
//检查电源是否为奇数
如果(uiPower&1){
uiResult=((uiResult%uiLargePrime)*(uiXVal%uiLargePrime))%uiLargePrime;
}
//现在,权力是平等的
uiPower=uiPower>>1;
uiXVal=((uiXVal%uiLargePrime)*(uiXVal%uiLargePrime))%uiLargePrime;
}
返回结果;
}
//拉宾-卡普算法
void RabinKarpAlgo(标准::字符串和文本,标准::字符串和模式){
std::矢量位置;
//计算模式的哈希值。
sCalcHash散列;
std::uint64\u t hashValPattern=散列(模式);
问题是我用无符号std64整数计算mod,所以mod变为正,这取决于实现
参考:C++03第5.6段第4条:
二进制/运算符产生商,二进制%运算符产生第一个表达式除以第二个表达式的余数。如果第二个操作数/或%为零,则行为未定义;否则(a/b)*b+a%b等于a。如果两个操作数都是非负的,则余数是非负的;如果不是,则余数的符号由实现定义
因此,为了避免这个问题,我在下面尝试将大素数数据类型更改为int64,它在下面工作并完成
std::int64_t iHashValRecur = ( (Text[uiIdx] % uiLargePrime) +
((uiXValue % uiLargePrime * hashValLastIdx % uiLargePrime) % uiLargePrime) -
((Text[uiIdx + uiPatternLength] % uiLargePrime * (uiXExpVal % uiLargePrime)) % uiLargePrime)
);
std::int64_t iHashVal = hash(Text.substr(uiIdx, uiPatternLength));
iHashValRecur = iHashValRecur % uiLargePrime;
while (iHashValRecur < 0) {
iHashValRecur += uiLargePrime;
}
iHashValRecur = iHashValRecur % uiLargePrime;
std::int64\t iHashValRecur=((Text[uiIdx]%uiLargePrime)+
((uiXValue%uiLargePrime*hashValLastIdx%uiLargePrime)%uiLargePrime)-
((文本[uiIdx+uiPatternLength]%uiLargePrime*(uiXExpVal%uiLargePrime))%uiLargePrime)
);
std::int64_t iHashVal=hash(Text.substr(uiIdx,uiPatternLength));
IHashValRecurr=IHashValRecurr%uiLargePrime;
而(ihashvalrecurr<0){
IHashValRecurr+=uiLargePrime;
}
IHashValRecurr=IHashValRecurr%uiLargePrime;