C++ 基于正倒排索引的搜索引擎 Searcher 模块详解

3. 合并与排序

将哈希表中聚合好的数据转移至向量 inverted_list_all，并根据权重从高到低排序，确保高相关度文档优先展示。

std::vector<InvertedElemPrint> inverted_list_all;
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;
});

4. 构建 JSON 结果

遍历排序后的文档列表，通过正排索引获取标题、URL 等内容，并使用 JsonCpp 库将其序列化为 JSON 字符串返回给前端。

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);

摘要生成策略

为了提升用户体验，搜索结果需附带关键词相关的上下文摘要。GetDesc 函数在 HTML 内容中定位关键词位置，截取前后固定长度的文本片段。若未找到关键词或长度不足，则返回默认提示。

std::string GetDesc(const std::string& html_content, const std::string& word) {
    int prev_step = 50;
    int next_step = 100;
    // 忽略大小写查找关键词
    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;
}

数据结构设计

为解决多关键词匹配导致的文档重复问题，设计了 InvertedElemPrint 结构体。它作为去重与信息聚合的载体，以 doc_id 为键，配合哈希表确保同一文档在结果集中仅出现一次，同时累积匹配到的所有关键词及其权重。

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

完整代码参考

以下为 Searcher 模块的完整头文件实现：

#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;
        }
    };
}