little_tools/subgraph.cpp

// =====================================================================================
//
//       Filename:  subgraph.cpp
//
//    Description:  output subgraph
//
//        Version:  1.0
//        Created:  2018年 01月 08日 星期一 16:09:22 CST
//       Revision:  none
//       Compiler:  g++
//
//         Author:  Jinkun Lin, jkunlin@gmail.com
//   Organization:  School of EECS, Peking University
//
// =====================================================================================
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;

vector<vector<int>> adjacency_list;

// read graph file into adjacency_list
void fast_read(string file_name) {
	ifstream in_file(file_name);
	if (!in_file) {
		cout << "in_file error" << endl;
		exit(1);
	}
	in_file.seekg (0, in_file.end);
	size_t file_len = in_file.tellg();
	in_file.seekg (0, in_file.beg);
	char *data = new char [file_len];

	in_file.read(data, file_len);
	in_file.close();

	data[file_len - 1] = '\0';

	//skip comments
	char *pos = data;
	while (*pos == 'c') {
		while(*(pos++) != '\n');
	}

	//read vertex_count
	int vertex_count = 0, edge_count = 0;
	while (*pos < '0' || *pos > '9') {
		++pos;
	}
	while (*pos != ' ') {
		vertex_count = vertex_count * 10 +  *pos - '0';
		++pos;
	}
	//read edge_count
	while (*pos < '0' || *pos > '9') {
		++pos;
	}
	while (*pos >= '0' && *pos <= '9') {
		edge_count = edge_count * 10 +  *pos - '0';
		++pos;
	}

	//read adjacency_list
	adjacency_list.resize(vertex_count + 1);

	vector<int> vertex_degree(vertex_count + 1, 0);
	char *stash_pos = pos;
	int v1, v2;
	for (int i = 0; i < edge_count && *pos != '\0'; ++i) {
		v1 = v2 = 0;
		//read v1
		while (*pos < '0' || *pos > '9') {
			++pos;
		}
		while (*pos != ' ') {
			v1 = v1 * 10 +  *pos - '0';
			++pos;
		}
		//read v2
		while (*pos < '0' || *pos > '9') {
			++pos;
		}
		while (*pos >= '0' && *pos <= '9') {
			v2 = v2 * 10 +  *pos - '0';
			++pos;
		}
		vertex_degree[v1]++;
		vertex_degree[v2]++;
	}
	for (size_t v = 1; v < adjacency_list.size(); ++v) {
		adjacency_list[v].reserve(vertex_degree[v]);
	}
	pos = stash_pos;
	for (int i = 0; i < edge_count && *pos != '\0'; ++i) {
		v1 = v2 = 0;
		//read v1
		while (*pos < '0' || *pos > '9') {
			++pos;
		}
		while (*pos != ' ') {
			v1 = v1 * 10 +  *pos - '0';
			++pos;
		}
		//read weight
		while (*pos < '0' || *pos > '9') {
			++pos;
		}
		while (*pos >= '0' && *pos <= '9') {
			v2 = v2 * 10 +  *pos - '0';
			++pos;
		}
		adjacency_list[v1].push_back(v2);
		adjacency_list[v2].push_back(v1);
	}
	delete[] data;
}

int main(int argc, char const *argv[]) {
	if (argc != 2) {
		std::cout << "usage" << std::endl;
		return 1;
	}
	string input_filename =argv[1];
	fast_read(input_filename);

	vector<int> vertex;
	int v;
	vector<int> indicator(adjacency_list.size(), 0);
	std::cout << "input vertex:" << std::endl;
	while (cin >> v) {
		if (indicator[v] == 0) {
			vertex.push_back(v);
			indicator[v] = 1;
		}
	}
	std::sort(vertex.begin(), vertex.end());

	for (auto v : vertex) {
		std::cout << v << " : ";
		for (auto u : adjacency_list[v]) {
			if (indicator[u]) {
				cout << u << ' ';
			}
		}
		std::cout << std::endl;
	}
	return 0;
}