// An inverted index of a string is building a data structure that
// maps each word to positions where that word appears.
#include <iostream>
#include <string>
#include <unordered_map>
#include <vector>
#include <sstream>
#include <algorithm>
// ------------------------------------------------------------
// cleanWord
// Removes punctuation and converts to lowercase.
// This ensures consistent indexing.
// ------------------------------------------------------------
std::string cleanWord(const std::string& word) {
std::string cleaned;
for (char c : word) {
if (std::isalnum(static_cast<unsigned char>(c))) {
cleaned += std::tolower(c);
}
}
return cleaned;
}
// ------------------------------------------------------------
// buildInvertedIndex
// Creates an inverted index mapping each word to the positions
// where it appears in the input string.
// ------------------------------------------------------------
std::unordered_map<std::string, std::vector<int>>
buildInvertedIndex(const std::string& text) {
std::unordered_map<std::string, std::vector<int>> index;
std::istringstream iss(text);
std::string word;
int position = 0;
while (iss >> word) {
std::string cleaned = cleanWord(word);
if (!cleaned.empty()) {
index[cleaned].push_back(position);
}
position++;
}
return index;
}
int main() {
std::string text =
"Imagine all the people living for today. "
"Imagine there's no heaven. Imagine all the people.";
// Build the inverted index
auto index = buildInvertedIndex(text);
// Print the inverted index
std::cout << "Inverted Index:\n";
for (const auto& entry : index) {
std::cout << entry.first << ": ";
for (int pos : entry.second) {
std::cout << pos << " ";
}
std::cout << "\n";
}
}
/*
run:
Inverted Index:
heaven: 10
no: 9
today: 6
living: 4
theres: 8
people: 3 14
the: 2 13
all: 1 12
for: 5
imagine: 0 7 11
*/
