C++ 搜索引擎核心：基于正倒排索引的 Searcher 实现解析

3. 摘要提取 (GetDesc)

此函数负责在 HTML 内容中定位关键词，截取前后片段生成摘要。如果内容长度不足或找不到关键词，则返回特定标识。

std::string GetDesc(const std::string& html_content, const std::string& word) {
    int prev_step = 50;
    int next_step = 100;
    
    // 忽略大小写查找子序列
    auto iter = std::search(html_content.begin(), html_content.end(), 
                            word.begin(), word.end(), 
                            [](int x, int y){ return (std::tolower(x) == std::tolower(y)); });
    
    if (iter == html_content.end()) return "None1";
    int pos = std::distance(html_content.begin(), iter);
    if (pos == std::string::npos) return "None1";

    int start = 0;
    int end = html_content.size() - 1;
    
    // 防止越界访问
    if (pos - prev_step > start) start = pos - prev_step;
    if (pos + next_step < end) end = pos + next_step;
    
    if (start >= end) return "None2";
    
    std::string desc = html_content.substr(start, end - start);
    desc += "...";
    return desc;
}

4. 结构体设计 (InvertedElemPrint)

InvertedElemPrint 主要用于解决重复文档问题。当同一文档匹配多个关键词时，它借助哈希表的键唯一性，确保文档在结果集中只被记录一次，同时聚合权重信息。

struct InvertedElemPrint {
    uint64_t doc_id;
    int weight;
    std::vector<std::string> words;
    InvertedElemPrint() : doc_id(0), weight(0) {}
};

5. 完整代码参考

以下是整合后的完整类定义，涵盖索引初始化、搜索逻辑及摘要生成。

#pragma once
#include "index.hpp"
#include "usuallytool.hpp"
#include <algorithm>
#include <jsoncpp/json/json.h>
#include "log.hpp"

namespace ns_searcher {
    struct InvertedElemPrint {
        uint64_t doc_id;
        int weight;
        std::vector<std::string> words;
        InvertedElemPrint() : doc_id(0), weight(0) {}
    };

    class Searcher {
    private:
        ns_index::Index* index;
    public:
        Searcher(){}
        ~Searcher(){}

        void InitSearcher(const std::string& input) {
            index = ns_index::Index::Getinstance();
            index->BuildIndex(input);
            LOG1(NORMAL, "建立索引成功...");
        }

        void Search(const std::string& query, std::string* json_string) {
            std::vector<std::string> words;
            ns_util::JiebaUtil::CutString(query, &words);

            std::vector<InvertedElemPrint> inverted_list_all;
            std::unordered_map<uint64_t, InvertedElemPrint> tokens_map;

            for (std::string w : words) {
                boost::to_lower(w);
                ns_index::InvertedList* inverted_list = index->GetInvertedList(w);
                if (inverted_list == nullptr) continue;

                for (const auto &elem : *inverted_list) {
                    auto &item = tokens_map[elem.doc_id];
                    item.doc_id = elem.doc_id;
                    item.weight += elem.weight;
                    item.words.push_back(elem.word);
                }
            }

            for (const auto &item : tokens_map) {
                inverted_list_all.push_back(std::move(item.second));
            }

            std::sort(inverted_list_all.begin(), inverted_list_all.end(), 
                      [](const InvertedElemPrint &e1, const InvertedElemPrint &e2){
                          return e1.weight > e2.weight;
                      });

            Json::Value root;
            for (auto& item : inverted_list_all) {
                ns_index::DocInfo* doc = index->GetForwardIndex(item.doc_id);
                if (doc == nullptr) continue;
                
                Json::Value elem;
                elem["title"] = doc->title;
                elem["desc"] = GetDesc(doc->content, item.words[0]);
                elem["url"] = doc->url;
                root.append(elem);
            }
            
            Json::StyledWriter writer;
            *json_string = writer.write(root);
        }

        std::string GetDesc(const std::string& html_content, const std::string& word) {
            int prev_step = 50;
            int next_step = 100;
            
            auto iter = std::search(html_content.begin(), html_content.end(), 
                                    word.begin(), word.end(), 
                                    [](int x, int y){ return (std::tolower(x) == std::tolower(y)); });
            
            if (iter == html_content.end()) return "None1";
            int pos = std::distance(html_content.begin(), iter);
            if (pos == std::string::npos) return "None1";

            int start = 0;
            int end = html_content.size() - 1;
            
            if (pos - prev_step > start) start = pos - prev_step;
            if (pos + next_step < end) end = pos + next_step;
            
            if (start >= end) return "None2";
            
            std::string desc = html_content.substr(start, end - start);
            desc += "...";
            return desc;
        }
    };
}